Triple-Stage-Actuator System with Thin-Film Coil for Head-Positioning Control in Hard Disk Drives
Publication Date: 2014-Jan-24
The IP.com Prior Art Database
Disclosed is a triple-stage actuator system with a thin-film coil actuator (called “film actuator”) for hard disk drives. The film actuator is attached to a coil of Voice Coil Motor (VCM). In this proposed control system, the first stage is a VCM actuator, the second stage is a PZT actuator for moving the suspension, and the third stage is the film actuator to control the coil-torsion mode. The proposed triple-stage actuator system can compensate for the vibration of coil-torsion mode by the film-actuator loop instead of using the notch filter in VCM loop. Comparison of sensitivity functions showed that the triple-actuator system can improve the sensitivity function at frequency of the coil-torsion mode by about 7 dB.
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In the head-positioning system of hard disk drives (HDDs), various mechanical resonances may lead to degrade the performance of the control system. Among other things, a coil-torsion mode around 3 kHz has a large potential risk because its resonant frequency is located in unstable phase area of the head-positioning control system.
To overcome this issue, a thin-film coil actuator (called "film actuator") was proposed in reference . Figure 1 shows the basic schematic of the film actuator. Figure 2 shows a photograph of the film actuator attached to a coil of Voice Coil Motor (VCM).
Figure 1: Basic schematic of this film actuator.
Figure 2: Photograph of VCM coil with thin-film actuator.
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2. Triple-stage-actuator system with film actuator
In this invention, we propose a triple-stage actuator system with the film actuator. Figure 3 shows the basic schematic of the triple-stage actuator. The first stage actuator is a VCM actuator, the second one is a PZT actuator for moving the suspension, and the third one is the film actuator to control the coil-torsion mode. The block diagram of the triple-stage actuator system for the head-positioning control is shown in Figure 4. Where, Pvmeans the transfer characteristics from the VCM-actuator input to the head position, Pp means that from the PZT-actuator input to the head position, and Pf means that from the film-actuator input to the head position. Cv means a controller for the VCM actuator, Nv means multi-rate notch filter for the VCM actuator, Cp is a controller for PZT actuator, Np is a multi-rate notch filter for PZT actuator, Cf is a controller for the film actuator, H is a zero-order hold (ZOH), and S is a sampler. The sampling frequency of H and S are set as 43.2 kHz. The number of heads is ten in this control system.
Figure 3: Triple-stage actuator with Film actuator.
Figure 4: Block diagram of triple-stage actuator system.
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The measured frequency responses of the Pv and Pp are shown in Figures 5 and 6, respectively. The measured frequency response of Pf is shown in Figures 7 (over-all view from 1 kHz to 50 kHz) and 8 (zoom-in view from 3 kHz to 4 kHz). These results are measured by using a LDV (Laser Doppler Vibrometer) measurement system.
Figure 5: Frequency response of VCM actuator.
Figure 6: Frequency response of PZT actuator.
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Figure 7: Frequency response of film actuator (over-all view...