Microactuator Hysteresis Compensation via Inverse Digital Filter
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Solution Overview
Problem
Disc drives experience degraded servo performance due to hysteresis in microactuators, leading to non-linear behavior and errors in tracking and feedforward signals.
Innovation Solution
A hysteresis compensator using a digital filter based on an inverse Coleman-Hodgdon hysteresis model is implemented to linearize the effects of hysteresis in microactuators, characterized by measuring hysteresis curves with a servo controller in single-stage mode and applying DC voltage across the driving range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If microactuators are used to move read/write heads in disc drives, then positioning precision is improved, but hysteresis causes non-linear behavior that degrades servo performance
Solution Approach 1:
The patent applies preliminary action by characterizing the hysteresis of the microactuator before normal operation and pre-calculating compensation values. The servo controller characterizes hysteresis by driving the microactuator through its full range of motion and storing the measured hysteresis data. During actual servo operations, these pre-computed compensation values are applied to counteract the hysteresis effects, allowing the system to maintain high positioning precision while eliminating servo performance degradation.
2Stability of the object's composition
If hysteresis compensation is implemented using a digital filter and inverse model, then linearity of microactuator performance is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical hysteresis compensation mechanisms with a software-based digital filter implementation. Instead of using additional physical components or complex mechanical structures to compensate for hysteresis, the system uses a digital filter with coefficients derived from an inverse hysteresis model. This substitution of mechanical complexity with computational algorithms achieves the desired linearity improvement while minimizing the increase in overall device complexity.
3Measurement precision
If DC voltage is applied across the entire driving range to characterize hysteresis, then accuracy of hysteresis characterization is improved, but time required for characterization increases
Solution Approach 1:
The patent applies continuity of useful action by performing hysteresis characterization continuously during manufacturing and setup processes rather than as a separate, time-consuming procedure. The servo controller characterizes hysteresis by driving the microactuator through its full range of motion using DC voltage, and this characterization process is integrated into the normal system initialization sequence. By making the characterization continuous and automated, the system achieves high accuracy in hysteresis measurement while minimizing the time penalty, as the characterization can be performed during routine system startup or manufacturing testing.
Data Source
AI summary
Systems and methods for compensating for hysteresis in a disc drive are described. In one embodiment, a method may use an inverse hysteresis model to linearize effects of hysteresis of a microactuator in the disc drive. The hysteresis model may be a Coleman-Hodgdon hysteresis model. The hysteresis of the microactuator may be characterized, and the inverse hysteresis model may be based at least in part on the characterization. The inverse hysteresis model may be used to implement a digital filter. The digital filter may be employed in series with the microactuator to linearize the effects of hysteresis.