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Synchronization errors directly deteriorate the machining accuracy of metal parts and the existed method cannot keep high synchronization precision because of external disturbances. A new double position servo synchronous driving scheme based on semi-closed-loop cross-coupling integrated feedforward control is proposed. The scheme comprises a position error cross-coupling feedforward control and a load torque identification with feedforward control. A digital integrated simulation system for the dual servo synchronous drive system is established. Using a 20 t servo broacher, performance analysis of the scheme is conducted based on this simulation system and the simulation results show that systems with traditional parallel or single control have problems when the worktable works with an unbalanced load. However, the system with proposed scheme shows good synchronous performance and positional accuracy. Broaching tests are performed and the experimental results show that the maximum dual axis synchronization error of the system is only 8 μm during acceleration and deceleration processes and the error between the actual running position and the given position is almost zero. A double position servo synchronous driving scheme is presented based on cross-coupled integrated feedforward compensation control, which can improve the synchronization precision.

The inertia of the stacked multi-degree-of-freedom platform imposes limitation on the achievable motion speed. To overcome this barrier, the unstable design becomes very attractive. This research presents a novel single-deck dual-axis linear motor platform that is capable of fast long-range motion. The platform is equipped with air-bearing design to achieve backlash-free operation. As a result, the positioning rigidity depends entirely on the performance of the servo system. A force distribution control is used to decouple the difference axis dynamics. This research also proposes a chain scattering description (CSD) setup to allow a pseudo-derivative feedback (PDF) control framework that is commonly used in industrial motion control for achieving high servo rigidity. An interesting finding is that our experiments show that without the help of complex piggyback piezoelectric stage, the single-deck platform design, with a stroke as large as 20 mm, can already reach a servo accuracy of ±60 and ±80 nm in the x- and y-axis and 600 μarcsec in the yaw axis.

Dual-stage servo control loops are modeled for hard disk drives (HDDs) with the consideration of time delay which is due to the time taken for position error signal measurement and controller computing. The time delays are involved in controller design and the closed servo control loop is investigated to show the effects of the time delay on servo control performance. The studied actuation system is a PZT milliactuator based dual-stage servo system. The delay time within and over the sampling interval is separately considered for 62.5 kHz sampling rate. To show the effect of sampling rate on servo control performance, a control system designed with 40 kHz sampling rate is also studied. As a result, significant improvement of servo performance is attained with this increased sampling rate and a reasonable time delay for the dual-stage actuation system.

The position error signal (PES) in current hard disk drives is generated from the embedded servo data and used as the input for the track following controller. The servo pattern design and the decoding are both quite complicated in terms of the servo writing and servo detection, but they are important for the system dynamics study and track following controller design. In this paper, a novel scheme based on discrete fourier transformation (DFT) to decode the servo signal from a special magnetic servo pattern and generate the PES is proposed. In the scheme adjacent magnetic tracks with different frequencies are recorded to the disk and used as servo tracks to encode the position information. Simulation results show that the amplitudes at the two writing frequencies in the readback spectrum depend on the magnetic head position. The quadrature PES defined by the difference of the amplitudes is almost linear between the two adjacent tracks The simulation and off-line experimental results analysis agree with each other and prove the feasibility of this scheme. A real-time signal acquiring and processing system with a commercial field programmable gate array (FPGA) and ADC/DAC chips was built, and the proposed scheme was implemented in the FPGA to do the high-speed signal analysis. The magnetic head position information is extracted from the readback spectrum in the FPGA and transferred to a PC host for real-time graphic display using a labview interface. The system demonstrates an ability to generate the PES at 25 K samples per second with a resolution around 3 nm. The sampling rate can be enhanced further to 125 kHz if more servo sectors are written to the disk. This system provides a re-configurable research stage for studying the dynamic behavior of hard disk drives and for developing the control algorithm for track following.

This paper presents vibration reduction control of a voice coil motor (VCM) nano scanner. We had developed a VCM scanner. The scanner has flexure hinges structure. However, the VCM nano scanner has some problems of thermal drift and small damping compared to the PZT driven nano scanner. Especially, the small damping coefficient of the VCM scanner causes mechanical vibration when the control input signal is near to the resonance frequencies. Additionally, disturbance to the VCM scanner and electronic noise in the sensor also cause the mechanical vibration when they are near to the resonant frequencies. The mechanical vibration reduces the servo bandwidth as well as the accuracy, which deteriorates the AFM image of the samples. We design a pre-filter to reduce the signal applied to the VCM nano scanner and electronic noise in the sensor whose frequency is closed the resonant frequency of the VCM nano scanner. We measure the time and frequency response of the VCM scanner without using the pre-filter and with using the pre-filter. Finally, the topology images of a bare wafer are measured and compared using the AFM.

Holographic data storage is a strong candidate for the next generation archive storage device. However, disturbances such as external shock, vibration, flutter and eccentricity of the disk affects the holographic data storage device. Thus, tracking servo control is necessary in order to enhance the signal noise ratio and reduce the bit error rate and retrieve the data accurately. It is also inevitable to face track overlapping problem if there is no datum to apply servo control during the recording process. In this research, we suggest a method forming a holographic servo track to detect the tracking error signal continuously without using any additional laser diode or pre-format layer. The tracking servo controller is designed to improve the track following performance, and the validity of the proposed method is confirmed through experiments on our holographic data storage system.

In the NFR system, since the gap between SIL and disc is under 100 nm, the traditional servo method can not be applied, and its modification is necessary for the stable servo performance. The gap error servo method is well-known as a typical servo in the NFR system (Verschuren et al. in JJAP 44:3554–3558, 2005) for focusing direction, and pull-in procedure (Zijp et al. in IEEE Trans Magn 41(2):1042–1046, 2005) and hand-over (Lee et al. in JJAP 44(5B):3423–3426, 2005) methods are also good approaches for the stable servo in the near field. We can obtain a good servo performance using the gap error servo method, and its experimental result shows that it is consistent with the previous researches. In case of the track servo, 1-beam push pull was generally used for the traditional ODD. However, it contains a DC offset components with lens movement, and thus, we can not have a good RF signal and track error signal simultaneously. Therefore, in this paper we introduce the modified servo method, which uses gap error lens position and the successful servo result for surface disc and 1.7 μm cover layer disc. Test was performed with a 4-axis actuator, and it gives a good performance not only for gap and track servo, but also for radial and tangential tilt. Finally, we suggested the decoupling method between track-shift and tilt components using the gap error differential signal and the simple slit structure. Based on the experimental result, it was verified that slit structure can eliminate the track-shift component effectively.

Recently, the demand of the information storage devices with large storage capacity such as Blu-ray Disc and high-definition television is increased. In keeping with this trend, the optical storage devices are also required to have high data transfer rate and large storage capacity. To satisfy these requirements, the actuator for optical disc drive should have a high servo bandwidth to compensate the vibration of optical disc. The servo bandwidth is limited by some flexible modes of the actuator, thus it is essential to make these frequencies of flexible modes to high frequency region. The frequency of flexible mode depends on materials and shape. Stiff materials and simple shape is useful to increase the frequency of flexible mode. In this paper, we suggested a moving magnet type actuator having flexible modes which are happened at high frequency region. Generally, the moving magnet type actuator has an advantage to increase the frequency of flexible mode because the moving magnet type actuator has simple structure and the Young’s modulus of magnet is high. However, large moving mass and inefficiency of Electromagnetic (EM) circuit cut down driving sensitivities of actuator. To improve driving sensitivities, we designed the model with the closed EM circuit for tracking actuation. The design of experiments (DOE) procedure is applied to get proper design parameters and the variable metric method (VMM) which is a technique of optimization is used to improve driving sensitivity. The lens holder is also improved based on the optimization result of EM circuit. And to make up for the low efficiency of EM circuit, the thermal stability is checked on condition that the input current is very high. At last, the final design of moving magnet type actuator is suggested and it is verified that the driving performance and the structural stiffness of the final design is sufficient.

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.

This paper presents vibration reduction control of a voice coil motor (VCM)-driven actuator for SPM applications. We had developed a VCM nanoscanner. The scanner has flexure hinges structure. However, the VCM nanoscanner has some problems of thermal drift and small damping compared to the PZT driven nanoscanner. Especially, the small damping coefficient of the VCM nanoscanner causes mechanical vibration when the control input signal is near to the resonance frequencies of the scanner. Additionally, disturbance to the VCM scanner and electronic noise in the sensor also causes the mechanical vibration when they are near to the resonant frequencies. The mechanical vibration reduces the servo bandwidth as well as the accuracy, which deteriorates the AFM image of the samples. We design input shaping prefilter to reduce the signal applied to the VCM nanoscanner and electronic noise in the sensor whose frequency is close to the resonant frequency of the VCM nanoscanner. We measure the time and frequency response of the VCM scanner without using the prefilter and with using the prefilter. Finally, the topology images of a bare wafer are measured and compared using the AFM.

In feedback control systems, the anti-resonant zeros cannot be arbitrarily placed, hence degrading tracking performance as well as input disturbance and noise rejection capabilities due to reduced gain at the frequencies of the zeros. In this paper, an online adaptive inverse control with saturation (OAICS) algorithm is proposed for compensating the minimum phase resonant poles and anti-resonant zeros of a PZT active suspension using measured position error signal. Experimental results on a Φ-shaped PZT active suspension using laser Doppler vibrometer (LDV) shows the proposed OAICS is effective in cancelling the first two dominant minimum phase pole-zero pairs to achieve high servo bandwidth and low sensitivity servo system with small overshoot during set-point tracking.

Holographic data storage is a next generation data storage device, which has high storage density, high data transfer rate and short access time. The device is very sensitive to disturbances due to its enormous storage density. In the disk type holographic data storage device deviation occurs successionally on the position of the data as the disk rotates. Therefore the spot where the probe beam is illuminated should directly be corrected in order to exactly retrieve the desired data. In this paper we suggest a method using an additional beam containing a servo pattern in order to detect the deviation of the media. We also propose a real time servo control method to compensate the affect of the unpredicted disturbance.

The nano-motion actuator (NMA) had been designed for precise track following on a spin-stand which evaluated read and write performance of a high-density magnetic recording. A required specification of the original NMA was a resonance frequency of over 5 kHz and working distance of over 10 μm. However, according as industrial researches of the perpendicular magnetic recording progress, a phenomenon that is called WATER (Wide Area Track ERasure) should be evaluated on the spin-stand. Since required working distance to evaluate the WATER reaches to over 50 μm, an X–Y stage on the spin-stand was cooperated with the NMA, as usual. However, the piggyback system which combined the X–Y stage with the NMA could not observe the WATER phenomenon continuously on a disk medium. Therefore, a new NMA which had a large working distance of over 50 μm was required. The new NMA was designed and simulated several resonance modes by using 2D or 3D of EFM analysis. The new actuator called as NMA-k501 realized the working distance of 43.3 μm and the resonance frequency of 5.33 kHz with a mechanical damper. As wide servo bandwidth was reached to 2.75 kHz to apply a PID controller, clear and sharp step responses could be showed at a 1 and a 10 nm, respectively. Furthermore, when precise positioning stability was evaluated, the NMA-k501 was positioning within 0.101 nm at 3σ.

A servo design method is presented for high track-density computer disk drives, in which the plant time delay, mainly due to the processor computation time, is taken into account. The key idea is to incorporate the delay model into the output equation of the state-space representation of the plant model. The application results confirm that the proposed method is very effective in enabling a higher servo bandwidth and, thereby, in realizing nano-level control accuracy required in high track-density computer disk drives.

In Hard disk drive (HDD) single-stage servo system that uses voice coil motor as the sole actuator, the sensitivity hump appears unavoidable due to the Bode’s integral theorem, resulting in amplification of disturbances at frequencies higher than the open-loop gain crossover frequency. This paper studies the sensitivity transfer function limitation in HDD dual-stage servo system. A compensation method for the micro-actuator dynamics, termed as “near-perfect modeling” (NPM), is proposed to generate an effective compensated plant model with zero relative degree in order to suppress the sensitivity hump of the dual-stage servo loop. Therefore, high-frequency disturbances would not be amplified by the servo loop. Experimental results show that the sensitivity hump of dual-stage servo loop can be reduced to very close to 0 dB without amplification of the corresponding measurement noise.

A new air bearing linear actuator with a Voice Coil Motor (VCM) was investigated for a precise head track following in an Hard Disk Drive (HDD) magnetic recording tester system. The actuator has a servo bandwidth of two times as wide as that of a conventional HDD, due to a high stiffness without any friction. A low-pass filter was introduced to precisely monitor the step response behavior by reducing the relatively large noise of the used optical fiber sensor. The effect of the low-pass filter was investigated comparing with the other method. Track following accuracy was also tested by using a conventional 2.5-inch hard disk drive. The head installed on the actuator could follow on a track by using Position Error Signal (PES) from the servo pattern. When a Double Metal In Gap (D-MIG) head of 4 μm track-width was loaded on a disk rotating at 4200rpm, the tracking error could be compressed down to one-twentieth of the track-width. The tested system did not show any azimuth error of head-tracking due to the linear motion. In conclusion, the air-bearing linear actuator is suitable for a precise track following mechanism of a spin-stand tester for an HDD system.

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.

Currently, hard disk drives (HDD) use rotating disks to store digital data and magnetic recording heads are flying on the disk to read/write data. The recording heads are mounted on a slider–suspension assembly, which makes heads move from one track to another on the disk. The heads movement is controlled by close-loop feedback servo systems. It is well known that dynamic behaviors of head–slider–suspension-assembly (HSA) systems are of great influence on the track per inch capacity of HDD [1, 2]. As the problem is structurally complex, it is usually investigated using experimental methods or finite element simulation models [3]. Furthermore, the dual-stage servo system has been commonly considered as one promising solution to increase the servo bandwidth of the recording positioning system for high TPI HDDS. In particular, MEMS device embedded systems are superior to others in batch-fabrication. However, this dual-stage system has also resulted in more difficulties in predicting HDD dynamic performance. This paper presents the study of the problem using the macromodeling simulation approach. It applies efficient FEM based sub-structuring syntheses (SSS) [4] and fast boundary element method (BEM) approaches incorporated with system dynamics technology to investigate the dynamic characteristics of MEMS actuator embedded HSA systems for HDD.

The paper analyzes how the frequency bandwidth of a servo system is affected by the input voltage of its motor and the magnitude of the total backlash. The bandwidth of the system is defined as the set of antiresonance frequencies, which appears in the frequency-response characteristic. The change in the frequency-response characteristics is investigated depending on motor input voltage and the magnitude of the total backlash. It is shown that at infinite motor input voltage, the servo system has a bandwidth equivalent to that of a backlash-free system. The amount of the system’s bandwidth reduction due to the backlash changes greatly with the motor input voltage. It becomes possible then to determine the necessary maximum input voltage of the motor and the admissible magnitude of the total backlash to satisfy the desired bandwidth for a servo system with a gear reducer.

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.

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.

In this paper, we present a design method for a kind of general frequency dependent digital optimal preview servo system which is effective to improve frequency characteristics of closed loop system. By the method, for any rational expression frequency dependent weight which loads on error vector, we can design an optimal preview servo system. The result is applied to an air slide linear motor in simulation and its effectivity is proved.