Voice Coil Motor Research Articles

High precision tracking control of a servo gantry with dynamic friction compensation

This paper is concerned with the tracking control problem of a voice coil motor (VCM) actuated servo gantry system. By utilizing an adaptive control technique combined with a sliding mode approach, an adaptive sliding mode control (ASMC) law with friction compensation scheme is proposed in presence of both frictions and external disturbances. Based on the LuGre dynamic friction model, a dual-observer structure is used to estimate the unmeasurable friction state, and an adaptive control law is synthesized to effectively handle the unknown friction model parameters as well as the bound of the disturbances. Moreover, the proposed control law is also implemented on a VCM servo gantry system for motion tracking. Simulations and experimental results demonstrate good tracking performance, which outperform traditional control approaches.

초정밀 듀얼 스테이지를 위한 고댐핑 저진동 제어기 개발

In this study, a cross-damped low vibration controller was developed to reduce vibration in ultra-precision dual stage driven by master/slave principle. In master-slave structure, the master stage leads the driving motion and the slave stage follows it so as to maintain a constant gap between two stages. In this structure, a small perturbation of master stage makes big oscillations in slave servoing stage, so a low damped master stage composed of voice coil motor makes a long vibration in settling area after driving motion profile. In this research, an effective feedback damping algorithm for increase the damping characteristics of the dual stage was developed. The designed velocity damping algorithm improves the system stability and reduces the settling time of the whole system. Simulation and experimental results show that the developed algorithm reduces settling time and improves the regulating performance.

An electro-thermally activated rotary micro-positioner for slider-level dual-stage positioning in hard disk drives

Slider-level micro-positioners are useful to assist a voice coil motor to perform fine head positioning over a Tb/in2 magnetic disk. Recently, a new kind of slider-level micro-positioner was developed using the thermal unimorph of the Si/SU8 composite. It has the advantages of a very small footprint and high mechanical resonant frequency, but its stroke generation is inadequate, with a 50 nm dynamic stroke at 1 kHz. There is a need for a larger thermally induced stroke. This paper presents a rotary design of an electrothermal micro-positioner to address the stroke requirements without consuming more power or decreasing the mechanical resonant frequency. Experimental studies show the present rotary design can produce a six-fold larger displacement, as compared to the previous lateral design, while possessing a 35 kHz resonant frequency. In addition, simple analytical models were developed to estimate: (i) the rotational stiffness and system’s natural frequency, (ii) thermal unimorph bending and stage rotation, and (iii) the system’s thermal time constant for this rotary electro-thermal micro-positioner. This study found that this rotary electro-thermal micro-positioner can meet the basic stroke requirement and high mechanical resonant frequency for a moving slider, but its thermal cut-off frequency needs to be increased further.

Multi-mode sliding mode control for precision linear stage based on fixed or floating stator

This paper presents the control performance of a linear motion stage driven by Voice Coil Motor (VCM). Unlike the conventional VCM, the stator of this VCM is regulated, which means it can be adjusted as a floating-stator or fixed-stator. A Multi-Mode Sliding Mode Control (MMSMC), including a conventional Sliding Mode Control (SMC) and an Integral Sliding Mode Control (ISMC), is designed to control the linear motion stage. The control is switched between SMC and IMSC based on the error threshold. To eliminate the chattering, a smooth function is adopted instead of a signum function. The experimental results with the floating stator show that the positioning accuracy and tracking performance of the linear motion stage are improved with the MMSMC approach.

Iterative learning control of high-acceleration positioning table via sensitivity identification

Through the convergence analysis of the iterative learning control, it can be seen that the inverted model of the sensitivity can be used as the update law of iterative learning controller. However, due to the little knowledge in modeling uncertainty and in feedback controllers embedded in drivers with hard-to-obtain parameters, it is difficult to directly calculate the transfer function of the sensitivity. To solve this problem, this article presents sensitivity identification–based iterative learning controller for a high-acceleration positioning table actuated by the voice coil motors. In the sensitivity identification process, a frequency sweep signal was exerted to the closed-loop system as the equivalent disturbance, and the perturbation of the tracking error was gathered as output data. Then, the autoregressive model of the sensitivity was gained conveniently. Finally, the proposed sensitivity identification–based iterative learning controller was implemented in the experimental setup with the maximum acceleration of 5.3 g. The experimental results show that the tracking error of the X- and Y-axes decreased from 530 and 2480 µm to 6 and 18 µm, respectively, after the third iteration of the proposed iterative learning controller method, and the identified sensitivity can be easily designed in the iterative learning controller to greatly improve the tracking performance.

Design and Control of a Novel Fast Tool Servo Used in Diamond Turning of Freeform Optics

Optical free-form surfaces are becoming more and more popular in the industry application, which can be fabricated by diamond turning based on fast tool servo (FTS). It is an efficient, precise and low-cost processing method. In order to use diamond turning to fabricate the freeform optics, this paper develops a novel long range fast tool servo which is actuated by voice coil motor. The total range can reach up to 30 mm. The important parts of the FTS have been simulated and analyzed. The transfer function model identification of the FTS has been accomplished. Since the desired tool trajectories are approximately periodic signals in freeform surfaces turning, and the adaptive feedforward cancellation (AFC) control can achieve perfect tracking and disturbance rejection of periodic signals, the AFC control is designed to be added on the IMC-PID controller.

Saturated Output Regulation Approach for Active Vibration Control of Thin-Walled Flexible Workpieces With Voice Coil Actuators

Thin-walled flexible workpieces are known to be the most commonly used flexible elements in mechanical structures and machines in the industries of aerospace, national defense, petrochemistry, and so on. Workpiece machining vibrations induced by machining tools greatly worsen the efficiency and accuracy of milling processes, and hence, vibration attenuation has become a bottleneck for improving the machining quality of thin-walled flexible workpieces. An active vibration control system is hereby established to attenuate vibration by using laser displacement detectors and voice coil motors (VCMs). In this paper, we reveal that the vibration attenuation problem can be theoretically formulated as an output regulation problem subject to saturated actuation of VCMs. Within the formulation, a saturated output regulation algorithm is successfully implemented and its effectiveness is extensively examined by experiments.

Development and Modeling of a Macro/Micro Composite Positioning System for Microelectronics Manufacturing

A macro-micro composite positioning stage with high acceleration and high precision is presented in this paper. A linear voice coil motor (VCM) is used to generate the macro motion, and a piezoelectric (PZT) actuator is adopted to drive the micro stage to achieve a precision micro motion, while PZT actuator can also be used to compensate the position error. A high-resolution grating is integrated into the stage to establish the closed-loop feedback. To research the mechanical dynamic characteristic of the stage, the mechanical dynamic model of the macro mechanism and micro mechanism are established, which is based on the rigid-flexible mixed dynamics of mechanical system. The dynamic characteristics of macro motion and micro motion are studied in detail, which is based on the mechanical dynamic simulation of Matlab. The accuracy of the established dynamic model and the performance of the stage are tested by using the scanning laser vibrometer. Both of the simulation results and test results show that the established model can well reflect the dynamic characteristics of the macro-micro composite positioning stage. It also indicates that the developed stage can well achieve a high acceleration and high precision motion, which aims to be applied in microelectronics manufacturing.

A novel long range fast tool servo for diamond turning

Single point diamond turning (SPDT) based on tool servo system is one of the significant techniques to fabricating the optical freeform surfaces. The conventional fast tool servo (FTS) actuated by piezoelectric actuator has the problem of short stroke, while the drawback of the slow tool servo (STS) is low frequency response. This paper briefly presents a novel long range fast tool servo (LRFTS) with high frequency response and long stroke. The total stroke can reach up to 30 mm. The LRFTS uses a voice coil motor as the actuating element and air bearings as the guide mechanism. The LRFTS utilizes a linear encoder to measure the displacement of the tool for closed loop control. The servo performance of the LRFTS system’s amplitude and frequency response is analyzed. The physical model of the LRFTS is identified. A series of experiments have been conducted to verify the performance of the designed LRFTS. Micro-lens array fabrication experiments on an aluminum part are conducted using the designed LRFTS. The factors influencing the surface roughness have been analyzed.

Mechanisms of Minimum Skew Angle Actuation for Hard Disk Drives

The utilization of voice coil motor (VCM) rotary actuator in hard disk drives (HDDs) results in skew angles between the read/write head and disk rotation direction. The system performance and achievable capacity of hard disk drives are excessively sensitive to the skew angle [1–3]. The difference in skew angle, between the ID to the OD can be as large as more than 30 degrees in conventional 3.5” and 2.5” VCM actuated HDDs. This paper presents three mechanisms, namely, a slant arm/suspension mechanism, a guider track mechanism, and a 4 link mechanism which can be designed to achieve minimum skew angle actuations for hard disk drives. The slant arm/suspension mechanism reduces the skew angle to ± 2 degrees in rotary actuated systems. The guider track mechanism further achieves the skew angle as zero degree theoretically. As an approximation of the guider track mechanism, the 4 link actuation mechanism reduces the skew angle to 0.4 degree. Their system dynamic behaviors are studied numerically using finite element modelling. Some of designs are prototyped and experimentally investigated.

弾性ヒンジを用いたアクティブ制御型油静圧スラスト軸受に関する研究

弾性ヒンジを用いたアクティブ制御型油静圧スラスト軸受に関する研究

ゼロコンプライアンス機構を利用した三分力測定装置の開発

Zero-compliance mechanism is applied to force measurement. In the proposed measurement system, force is estimated from the displacement of a detection point without displacing the point of force. The efficacy was proved by an experimental apparatus that uses double series magnetic suspension. In addition, a 3-component force measurement appratus was fabricated which combines four single-axis measurement units, each of which uses parallel springs and a voice coil motor as an actuator. However, the accuracy of measurement was limited mainly because of some interaction among the four units. To solve such a problem, a new apparatus for 3-component force measurement is designed and fabricated. It has a common detection point for three components. Force measurements were carried out with the apparatus. The results show that 3-component forces were measured with a high resolution by the developed apparatus.

Multi-rate Observer Based Sliding Mode Control with Frequency Shaping for Vibration Suppression Beyond Nyquist Frequency

Abstract: Nyquist frequency limits the frequency range of the continuous-time signals that can be reconstructed through the sampled discrete-time signals. In hard disk drives (HDDs), there exist resonance modes near and beyond the Nyquist frequency in the voice coil motor (VCM). Such resonance modes, if excited, may generate vibration beyond the Nyquist frequency which would seriously degrade the servo performance. To capture such vibration, a multi-rate extended observer is designed based on the nominal dynamic model of the excitation process. This observer estimates both the states and the vibration at a fast rate based on the sampled position error signal (PES) at a slow rate. The estimated states are utilized to design a sliding mode control algorithm at the fast rate with frequency shaping to suppress vibration beyond the Nyquist frequency. Meanwhile, the estimated vibration are incorporated in the control signal to further compensate the actual vibration. Simulation results demonstrate the benefits of the proposed algorithm: large off-track behaviors of the VCM are mostly detected and the vibration beyond the Nyquist frequency are suppressed.

Suppression of resonance in hard disk drive servo system with feedback resonant controller: a benchmark model study

In order to achieve the precision desired, the bandwidth of the read-write head positioning servomechanism of hard disk drive (HDD) is required to be very high to minimise the effects of external disturbances. However, any attempt to increase the bandwidth is hindered by increased gain in frequencies of mechanical resonances leading to oscillatory response. If not compensated properly, excessive or unbounded oscillation may even lead to instability. Cascade compensation is the popular method for compensating multiple resonant modes. However, this method requires a very precisely identified plant model. On the contrary, feedback controller works better in such situation which does not require a very accurate plant model. This paper presents a feedback resonant controller designed in a simple way to suppress the resonant modes of voice coil motor (VCM) actuator used in HDD servo system. Simulation results substantiate the effectiveness of the proposed design methodology.

Relationship between flying-height and tracking-position control with thermal actuators for magnetic heads in HDDs

Abstract: To increase a servo bandwidth of a head-positioning control system in hard disk drives, a triple-stage actuator system was developed with thermal actuators. This positioning control system consists of a voice coil motor (VCM), piezoelectric (PZT) actuators, and a thermal-positioning actuator. The thermal-positioning actuator is good for control in high frequency range because it has little negative impact caused by mechanical resonances. However, the thermal-positioning actuator causes flying-height fluctuations that may lead to worsening of the magnetic recording performances. To overcome this issue, this paper presents a control system that employs the feedforward control scheme on a thermal flying-height control system. Simulation results showed that the proposed method was able to compensate for the flying-height fluctuations during the track-following control by about 87 %.

바코드 리더용 스캐닝 미러를 위한 무빙 코일 타입 VCM 설계

바코드 리더용 스캐닝 미러를 위한 무빙 코일 타입 VCM 설계

A Phenomenon Discovered While Imaging Dolphin Echolocation Sounds

Our overall goal is to analyze dolphin sounds to determine if dolphins utilize language or perhaps pictorial information in their complex whistles and clicks. We have recently discovered a novel phenomenon in images derived from digital recordings of the sounds of dolphins echolocating on submerged objects. Hydrophone recordings of dolphin echolocation sounds were input to a CymaScope, an analog instrument in which a water-filled, fusedquartz cell is acoustically excited in the vertical axis by a voice coil motor directly coupled to the cell. The resulting wave patterns were recorded with a digital video camera. We observed the formation of transient wave patterns in some of the digital video frames that clearly matched the shapes of the objects on which the dolphin echolocated, including a closed cell foam cube, a PVC cross, a plastic flowerpot, and a human subject. As further confirmation of this phenomenon the images were then converted into 3-dimensional computer models. The computer models were made such that the thickness at any given point was proportional to the brightness of a contrast-enhanced image with brighter areas thicker and darker areas thinner. These 3-dimensional virtual models were then printed in photopolymers utilizing a high definition 3D printer.

Development of a Compact Atomic Force Microscope Based on an Optical Pickup Head

Abstract: To develop a compact and cost-effective atomic force microscope (AFM), this paper proposes to utilize components of an optical pickup head of a CD/DVD player. One of the voice coil motors and the astigmatic detection system of the optical pickup head are employed to provide vertical actuation of an AFM cantilever and to measure its deflection. A flexure is installed on the optical pickup head to reduce the influence of ground vibrations and to change its actuator sensitivity for better AFM imaging. The feasibility of the proposed system is experimentally shown by recording a topography image of a standard calibration grating.

Composite Motion Design Procedure for Vibration Assisted Small-Hole EDM Using One Voice Coil Motor

To address the problem of debris accumulation in small-hole electrical discharge machine (EDM) and simplify the design of the spindle head, the paper proposes a novel composite motion design procedure integrated high frequency vibration and large stroke feed using one voice coil motor (VCM). Particularly, for the purposes of high servo accuracy and high frequency response of the composite motion, an improved zero-phase-error tracking controller (ZPETC) algorithm decoupled with the feedback controller is developed for the process control, in which the feedback parameter adjustment is very simple to reduce the computation complexity. At last, the proposed procedure is validated by the experimental study of the established VCM positioning table; the results verify the efficiency of the proposed method.

Earliest switch-on of dual-stage actuation in hard disk drives

In conventional track-settling process, dual-stage actuation (DSA) is not activated until the read/write head is in close proximity to the target track so that chances of saturation are reduced. In this paper, we propose an earliest switch-on scheme based on the calculation of the exact saturation boundary, considering both position error signal and voice coil motor velocity error. It allows the DSA loop to be switched on earlier than current practices while piezoelectric actuators remain unsaturated. Simulations on a 2.5$$''$$?? commercially available hard disk drive show that the proposed scheme can reduce the post-seek oscillation and shorten the 5 % track-settling time by more than 16 % in the presence of in-drive disturbances.