Design of hybrid type’s optical pickup actuator for system stability in high density reading and recording

Recently, there has been a trend to have large capacity and high data transfer rate in optical disk drive. Pickup actuator also should have high performance for satisfying this trend. Since moving magnet type actuator has more simple and robust structure than moving coil type one, we designed moving magnet type to accomplish high flexible mode frequency. However, the driving sensitivity of moving magnet type actuator was low because of its characteristics as following. At first, moving parts including magnets are heavy and electromagnetic (EM) circuits are not closed-loop owing to yoke composed of paramagnetic materials. Therefore, in order to increase the driving sensitivity without the degradation of the other dynamic characteristics, EM circuits were redesigned by adding solenoid coils on existing mechanism. As a result, the hybrid type actuator composed of moving magnet type and moving coil type was suggested to obtain high sensitivities and high flexible mode frequency. Design variables of EM circuits and structure parts were decided through parametric study and design of experiments procedure. Optimization algorithm using variable metric method was used to improve performance. Based on these results, the final model was presented.     

Improvement of dynamic characteristics for optical pickup actuator by magnetic circuit

 As disk rotational speed of optical disk drives (ODD) increases, an optical pickup actuator has a high servo bandwidth for its focusing and tracking control to follow dynamic disturbances by high rotational speed in ODD. However, the servo bandwidth is limited by some vibration modes due to the flexibility of the moving part in the actuator. In this paper, the influence of the driving forces generated by VCM on excitation of flexible modes of the moving part in high frequency range is analyzed. Especially, in order to reduce the first flexible mode affecting the servo bandwidth, it is attempted to modify force distribution on coils. The magnetic simulation is performed by using finite element analysis, and compared with experimental results. Finally, it is shown that flexible mode vibration can be suppressed by proper design of magnetic circuit. Received: 20 June 2002 / Accepted: 29 August 2002     

Development of symmetric type slim optical pickup actuator for flexible disk system

Recently, in information storage devices, several characteristics such as high data transfer rate, large storage capacity and small drive size are required as high-definition television (HDTV) broadcasting, mobile devices, and notebook personal computer (PC) were popularized. In optical disk drive (ODD), several actuators have been developed to satisfy these specifications. In this paper, we presented the symmetric type slim actuator with efficient tracking magnetic circuits for the flexible disk system. At first, electromagnetic (EM) circuits were designed to have big driving force for high sensitivities through design of experiments (DOE). And, in structural parts, we designed the actuator that had proper control bandwidth through several redesigns of moving parts. Consequently, the final model was fabricated and dynamic tests were experimented. And, it was checked that our actuator had a very high tracking sensitivity and could be applied to the flexible disk system.     

Improvement of dynamic characteristics for optical pickup actuator using sensitivity analysis

 The disk rotation speed of optical disk drives (ODD) has been increasing rapidly to achieve high data transfer rates. High servo bandwidths for focusing and tracking actuator are required to follow dynamic disturbance by high rotation speed in ODD. However, the servo bandwidth is significantly limited by some vibration modes which are induced by the flexibility of the moving part. In this work, the vibration modes affecting the bandwidth of actuators are shifted to high frequency range and suppressed by modifying the FE model which is used to analyze the motion of the actuator. Some local dimensions of the lens holder, which is included in the moving part, are selected as design variables to increase the stiffness without changing the material properties. Selected modal frequencies of the moving part are raised about 10%, while the performances of actuator such as DC and AC sensitivities are hardly affected by the modification. Received: 8 November 2001/Accepted: 18 March 2002 This work was supported by the Korea Science and Engineering Foundation (KOSEF) through the CISD at Yonsei University under grant No. 2001G0101.     

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.     

Hard disk drive seek-arrival vibration reduction with parametric damped flexible printed circuits

Seek-arrival track-mis-registration (TMR) is one of the most critical dynamic design factors for modern hard disk drives to achieve high data transfer-rate performance goal. With its flexible structural nature, the flex cable itself inevitably renders low-frequency natural modes which have been a challenge with respect to balancing design efforts among servo control, mechanical design, and manufacturing process in disk drive industry. In this paper, particular focus will be given to vibration damping approach to reduce flex cable related seek-arrival dynamics in a state of the art magnetic disk storage drive. Experimental parameter studies of a typical constrained-layer damped flex cable vibrations are presented with cable exposed to various damper length and fold in different geometries. Effectiveness of the damper is also demonstrated by frequency responses with random excitation from actuator arm. Several design options toward reducing the flex circuit related arrival TMR will also be discussed in this paper.     

Circuit model for piezoelectric actuator with electrically conductive epoxy

Dual stage actuator (DSA) has been a critical component in hard disk drives to increase servo control bandwidth and thus storage capacity. The electrical properties of a typical DSA vary with the frequency, as piezoelectric materials (e.g., PZT) and electrically conductive adhesives (ECA) are commonly used. A circuit model is thus needed to capture such complexity for servo control design. In this paper, we review two typical DSA circuit designs and compare three circuit models with different simplifications. The model with parallel RC circuits can successfully capture DSA circuit characteristics up to 1 MHz. Impedance data measured from real parts show excellent agreement with simulation results based on the model. In addition, we investigate impacts of abnormal ECA on the overall DSA transfer function. This research can provide a practical yet valuable guideline for DSA related servo control.     

Design of swing arm type actuators considering thermal and dynamic characteristics

The present state of the design of swing arm actuators for optical disc drives is to obtain the highly efficient dynamic characteristics within a very compact volume. As a necessary consequence, the need of the small form factor (SFF) storage device has arisen as a major interest in the information storage technology. Due to the size constraint, the thermal stability of the optical pick-up head is important: therefore, the actuator is designed to emit the heat, which is generated by the optical pick-up, along the structural body easily. In this paper, we suggest the miniaturized swing arm type actuator that has effective heat emission quality as well as satisfies the dynamic requirements for the SFF optical disk drive (ODD). The actuator is targeted to be installed in CF-II card size drive to be competitive with flash memory or mini hard disk drive used in mobile electric devices; therefore the dimension of the actuator is required as 11.0 mm × 2.5 mm × 25.0 mm (width × height × length). Because of its small size, the dynamic requirements are severe to ensure the enough gain-margin for the system control together with satisfying the DC/AC sensitivity conditions. Moreover, due to the small size, the maximum pick-up temperature is critical in design because the system has high possibility to reach the shut-down temperature. For the operating mechanism, it uses a tracking electromagnetic (EM) circuit for the focusing motion together and the initial model is designed and promoted by the design of experiments (DOE) only considering the dynamic characteristics. New concept design is suggested based on the topology optimization method considering the thermal conductivity. Furthermore, the new design is modified by DOE to maintain the high sensitivity and to have wide control bandwidth and decreasing mass and inertia. The final design of a swing arm type actuator for SFF ODD is suggested and its dynamic characteristics are verified.     

Frequency domain subspace identification of a tape servo system

As capacity demands for magnetic tape storage systems grow, servo actuator design for tracking data on high density tape media presents new modeling and control design challenges. In this paper a frequency weighted subspace identification algorithm is presented for control relevant model estimation of a tape servo actuator. Common to other subspace identification methods, the proposed algorithm is based on linear algebra techniques providing means for model order selection and model computation. The proposed subspace identification also allows for frequency dependent weightings to emphasize frequency data around the cross-over frequency to find models relevant for control design. The algorithm is applied to data obtained from a tape storage device, demonstrating model order selection and the estimation of servo actuator dynamics with control relevant model fit criteria.     

Design of swing arm actuator for small and slim optical disc drives

Recent advancements in mobile devices have fueled a requirement for information storage systems with characteristics such as subminiature size, low cost, and minimum power consumption. Small optical disk drives could provide a good solution, because their storage media is cheaper than those of hard disk drives or flash memories. In this paper, we proposed the miniaturized swing arm type actuator that had a new focusing mechanism for small and slim optical disk drives (ODD). Initial model was designed by EM and structural analyses. Based on results of DOE, optimization procedures of EM circuits were performed with design variables using variable metric method (VMM). And, structural parts were designed to maintain the high sensitivity of the actuator. Finally, the swing arm type actuator for small and slim ODDs was suggested and its dynamic characteristics were checked.     

基于ARM的超磁致伸缩微驱动器的偏置与驱动电路设计

超磁致伸缩微驱动器的工作主要需要提供一个可控的偏置磁场和驱动磁场,前者使超磁致伸缩材料的磁致伸缩特性得到优化,消除倍频效应,后者实现对微驱动器的输出位移控制;设计一个可控电流源,采用悬浮负载功率放大恒流电路,并通过ARM处理器的数模控制,使指定电流通过电磁线圈以产生所需磁场强度;该设计的可控电源,可输出最大±5A的电流,提供给偏置和驱动线圈,实现微驱动器的直观、灵活的控制。     

Integrated optimization design for high-speed three-axis actuator in optical pickup

Super-multi DVD drives are assumed to have the largest market share in the near future because of their high compatibility with all kinds of DVD/CD formats and high recording-reading speed at low cost. In this paper, we present a three-axis actuator used in a super-multi drive with a special magnetic circuit, consisting of symmetric driving coils and permanent magnets with proper placement. At first, the lens holder is optimized with sensitivity method to improve the flexible vibration modes in structure parts. Then, electromagnetic circuits are designed and optimized by Taguchi method and response surface methodology (RSM). Consequently, the final model is fabricated and tested by laser vibrometer system. The results verify the proposed actuator and the integrated design methods.     

Robust design of a microactuator for HDD head positioning

With rapid growth in areal recording density of hard disk drive (HDD), ultra-high precise head positioning and higher servo bandwidth are required. Dual-stage actuation system using MEMS actuator has been considered as one promising precise positioning solution. The microacatuator we designed has a low in-plane resonant frequency, which limits the servo bandwidth and needs compensation by servo control system. However, this resonant frequency may shift from its mean value during MEMS fabrication process. This shift adds difficulty to effective compensation for servo control. In this paper, a robust solution is proposed to minimize microactuator’s resonant frequency shift so that its first resonance frequency is insensitive to the effects of sources of processing variations and then effective compensation for high servo bandwidth can be achieved.     

双定子动磁铁式直线振荡执行器的力特性分析

为研究双定子动磁铁式直线振荡执行器的力特性,在分析执行器结构及运行原理的基础上,首先建立执行器的等效磁路模型,推导出一种计算执行器电磁推力及气隙磁链的解析模型,该模型充分考虑了结构参数及永磁体材料对电磁推力的影响;然后采用三维有限元参数化分析方法对执行器的电磁推力进一步分析和计算。结果表明:该执行器的电磁推力与动子位移无关,与定子电流成正比;气隙磁链是定子电流和动子位移的线性函数。研究结果将为该类新型执行器的优化设计及驱动控制提供较好的理论依据。     

一种光积分时间可调的线阵CCD驱动设计

设计了一种光积分时间可调的线阵CCD驱动电路,解决了由于光照强度变化而引起的图像失真问题。给出了线阵CCD图像采集硬件电路设计和光积分时间调节软件控制方法,可以在不改变系统时钟频率的前提下,通过改变移位脉冲的个数改变线阵CCD光积分时间。实验表明,该驱动电路设计灵活,稳定,完全能够满足要求。     

空间激光通信系统精跟踪单元PZT驱动电源的设计

压电陶瓷驱动电源是压电陶瓷微位移器应用中的关键部件。PA85是一种高电压、高功率MOSFET的带宽运算放大器,采用双电源供电,输出电流高达200mA,输出电压更可高达±215V。该文详细介绍了基于PA85的一种电源复合放大器的设计及仿真,通过对各项性能指标的仿真表明,该驱动电源具有精度高、分辨率高、稳定性好、纹波小和电路结构简单等优点。     

Design of an auto-focusing actuator with a flexure-based compliant mechanism for mobile imaging devices

There is increasing consumer’s demand for high-quality and high-performance mobile imaging devices. In this paper, an auto-focusing (AF) actuator with a flexure hinge that uses the electromagnetic (EM) circuit of a voice coil motor was designed and evaluated. The flexure hinge was designed by using finite element analysis. The EM circuit was designed based on the structural stiffness of the device. The EM circuit was analyzed using the design of experiments procedure. Based on the results, the effective design parameters were selected, and improvements were made to the design. Finally, a prototype of the AF actuator was manufactured, and the feasibility and performance of the actuator with the flexure hinge were verified experimentally. The experimental results indicated that the proposed actuator performed adequately and satisfied the design requirements.     

Charge control of parallel-plate, electrostatic actuators and the tip-in instability

Controlling the charge, rather than the voltage, on a parallel-plate, electrostatic actuator theoretically permits stable operation for all deflections. Practically, we show that, using charge control, the maximum stable deflection is limited by 1) charge pull-in, in which the actuator snaps due to the presence of parasitic capacitance and 2) tip-in, in which the rotation mode becomes unstable. This work presents a circuit that controls the amount of charge on a parallel-plate, electrostatic actuator. This circuit reduces the sensitivity to parasitic capacitance, so that tip-in is the limiting instability. A small-signal model of the actuator is developed and used to determine the circuit bandwidth and gain requirements for stable deflections. Four different parallel-plate actuators have been designed and tested to verify the charge control technique as well as to verify charge pull-in, tip-in, and the bandwidth requirements. One design travels 83% of the gap before tip-in. Another design can only travel 20% of the gap before tip-in, regardless of whether voltage control or charge control is used.     

Non-resonant electromagnetic wideband energy harvesting mechanism for low frequency vibrations

A novel non-resonant energy harvesting mechanism with wide operation frequency band is investigated for collecting energy from low frequency ambient vibration. A free-standing magnet is packaged inside a sealed hole which is created by stacking five pieces of printed circuit board substrates embedded with multi-layer copper coils. This device was tested under various acceleration conditions. Considering the air damping effect, two types of device structures with different covered plates are investigated. For type I, one covered acrylic plate with drilled air holes and another plate with no holes are used to package the moving magnet. For type II, the middle hole is sealed by two acrylic plates with drilled air holes. The output voltage of type II is better than the one of type I at the same acceleration. When the energy harvester of type II is shook at 1.9 g acceleration along longitudinal direction of the hole, the 9 mV output voltage with 40 Hz bandwidth, i.e., from 40 to 80 Hz, is generated. The maximum output power within the ranges of 40–80 Hz, i.e., operation bandwidth, is measured as 0.4 μW under matched loading resistance of 50 Ω. Experimental results show that type I device has wider frequency bandwidth, higher center frequency and smaller output voltage than type II device because type I device experiences severe damping influence.     

石英挠性加速度计表头力矩器噪声模型研究

石英挠性加速度计的内部力矩器噪声对于高精度的加速度计应用系统的影响是不可忽视的,但很少引起高度重视.针对高精度加速度计电路应用需要,研究了力矩器机械热噪声和力矩器线圈谐振的影响,建立了表头内部力矩器噪声电路模型,设计了测试电路,并对噪声电路模型进行了测试与验证.理论和实验结果均表明:机械热噪声产生的等效加速度对系统影响较小,力矩器线圈影响的谐振与驱动方式及驱动频率有关,脉宽调制(PWM)波驱动方式较正弦波驱动方式产生的谐振影响更大,当驱动频率靠近谐振点时,产生毫安(mA)级的谐振电流.模型的建立对石英挠性加速度计应用具有较好的参考价值.