RRO Compensation Lookup Table for Hard Disk Drive Positioning
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Solution Overview
Problem
Control systems, such as those in hard disk drives, face challenges in compensating for repeatable run-out (RRO) errors, which are recurring imperfections that affect the accuracy of position detection and control, leading to observable disturbances in output responses.
Innovation Solution
A control system with an RRO compensation module that determines the repeatable component of the error signal using a plant model and updates the target response by generating a correction value, which is added to the input signal to compensate for RRO, utilizing a lookup table or filter module to isolate and attenuate the repeatable component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RRO compensation is implemented using traditional methods, then measurement precision is improved, but device complexity increases due to requiring exact plant models and complex compensation algorithms
Solution Approach 1:
The patent replaces complex, precision-dependent plant models with simple lookup tables that store pre-measured RRO error patterns. These lookup tables act as 'cheap' computational objects that can be easily updated and require minimal processing power, eliminating the need for complex real-time calculations while maintaining compensation effectiveness.
Solution Approach 2:
The patent introduces lookup tables as an intermediary between the error detection mechanism and the compensation action. Instead of directly computing compensation based on complex plant models, the system uses lookup tables to map measured errors to corresponding correction values, simplifying the control architecture while preserving measurement precision.
2Manufacturing precision
If exact plant models are used for RRO compensation, then manufacturing precision is improved, but ease of manufacture deteriorates due to difficulty in obtaining accurate plant models
Solution Approach 1:
The patent performs RRO characterization and lookup table generation in advance, during system setup or manufacturing. By pre-measuring the specific RRO patterns of each drive and storing them in lookup tables before deployment, the system eliminates the need for complex real-time model identification, making the system easier to manufacture while maintaining high positioning accuracy.
Solution Approach 2:
The system characterizes its own RRO errors during initialization or manufacturing and stores this information in lookup tables for self-compensation. This self-service approach eliminates the need for external calibration equipment or complex model derivation processes, simplifying manufacturing while achieving high precision.
3Reliability
If complex compensation algorithms are implemented, then reliability is improved, but productivity deteriorates due to increased computational requirements
Solution Approach 1:
The patent segments the RRO compensation task into two parts: offline lookup table generation and online error correction. The computationally intensive segmentation and pattern recognition are performed once during table generation, while runtime operation requires only simple table lookups and additions, maintaining high reliability while improving processing speed and productivity.
Solution Approach 2:
The system updates lookup tables periodically during manufacturing or initialization phases, then uses these pre-computed tables for rapid real-time compensation. This periodic action separates heavy computation from continuous operation, ensuring both reliability through accurate compensation and productivity through fast execution.
Data Source
AI summary
A control system is configured to receive an input signal. The control system includes a control module to generate an output signal that tracks the input signal to the control system. The output signal includes a repeatable disturbance component. A compensation module is configured to receive an error signal. The error signal corresponds to a difference between the input signal and the output signal. The compensation module is configured to generate an estimate of the repeatable disturbance component based on the error signal, and to combine the estimate with the input signal to compensate for the repeatable disturbance component associated with the output signal.