Double Servo Magnetic Disc Actuator Decoupling
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Solution Overview
Problem
Conventional control systems in magnetic disc apparatuses, such as hard disc drives, face limitations in responding to increased densification due to narrow track pitches, leading to phase delays and unsatisfactory results, especially with the use of VCM control methods that rely on filters like lead lag and integration compensators, which restrict gain and outer-disturbance compression properties.
Innovation Solution
A magnetic disc apparatus employing a double servo system with a feedback controller that decouples the coarse and fine actuators, using a micro actuator like PZT and a voice coil motor, and optimizing the feedback path to achieve decoupled control, eliminating the need for low pass filters and other conventional components like integrators and lead lag filters, thereby stabilizing the system and enhancing disturbance compression characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional VCM control with filters (lead lag filter, integration compensator) is used to stabilize the actuator, then the actuator stability is improved, but phase delay occurs and gain is limited
Solution Approach 1:
The patent divides the control system into two independent control loops: one for the voice coil motor (VCM) and one for the piezoelectric actuator (PZT). Each actuator is controlled separately with its own feedback loop, allowing independent optimization of control parameters without the phase delays and gain limitations that occur when using filters in a unified control system.
Solution Approach 2:
The patent implements dynamic control by using a feedback mechanism that continuously adjusts the control signals based on real-time position information from the servo pattern. The control system dynamically compensates for disturbances and maintains optimal performance across varying operating conditions without requiring static filter-based compensation.
2Object-affected harmful factors
If filters are used in VCM control to improve outer disturbance property, then disturbance rejection is improved, but phase delay increases and gain is restricted
Solution Approach 1:
The patent employs feedback control where the position of the magnetic head is continuously measured using servo patterns and fed back to the control system. This feedback mechanism enables real-time compensation for external disturbances without requiring filter-based prediction, thereby maintaining high phase margins and gain while effectively rejecting disturbances.
3Productivity
If double servo system is introduced with decoupled control, then maximum performance is extracted, but control complexity increases
Solution Approach 1:
The patent segments the control system into two independent control loops, one for VCM and one for PZT, each with its own actuator-specific control parameters. This segmentation allows maximum performance extraction from each actuator type while simplifying the overall control architecture by eliminating the need for complex decoupling networks and reducing cross-interference between control channels.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for maximum performance extraction from the double actuator system, improving disturbance compression characteristics and achieving sufficient gains in low bands without phase loss, with the ability to optimize feedback amounts based on disturbance types for enhanced control.
Implementation Method 1
a fine actuator to hold a position of the magnetic head
Implementation Method 2
a coarse actuator to move the magnetic head above the magnetic disc by driving the arm
Data Source
AI summary
According to one embodiment, a magnetic disc apparatus includes a magnetic head which reads information stored in a magnetic disc, an arm which supports the magnetic head, and a feedback controller which controls a coarse actuator to move the magnetic head above the magnetic disc by driving the arm, a fine actuator to hold a position of the magnetic head, and a feedback path which feeds back a displacement of the actuator to a target value of the coarse actuator. The feedback controller controls decoupling of a double actuator system which adds up the coarse actuator and the fine actuator.