Windowed Delta-Sigma ADC Control for VCM Vibration Positioning
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Solution Overview
Problem
Existing data storage devices face challenges in accurately positioning the head over disk tracks due to vibrations and varying environmental conditions, which affect the performance of voice coil motor (VCM) controlled actuator arms, leading to reduced precision and increased noise during seek and tracking operations.
Innovation Solution
A windowed delta-sigma analog-to-digital converter (ADC) is configured to dynamically adjust its gain and window based on measured vibrations, enabling linear operation within a defined range and non-linear operation outside it, improving the digital current control loop's resolution, linearity, and noise reduction by adjusting the gain and window width according to environmental conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed gain ADC is used in the digital current control loop, then the circuit is simple, but the positioning precision deteriorates under varying vibration conditions
Solution Approach 1:
The patent implements a windowed delta-sigma ADC with dynamically adjustable gain and window width parameters. The gain is varied based on the amplitude of the position error signal (PES), and the window width is adjusted according to vibration levels detected by a sensor. This dynamic adaptation allows the ADC to maintain optimal resolution and linearity across different operating conditions, resolving the contradiction between fixed simplicity and variable precision.
Solution Approach 2:
The invention changes the operational parameters (gain and window width) of the ADC based on environmental conditions. When vibration is detected, the window width is increased and gain is adjusted to maintain measurement accuracy. This parameter adaptation enables the ADC to preserve high measurement precision without requiring a completely different hardware architecture for each condition.
2Measurement precision
If a high resolution ADC is used to improve positioning precision, then measurement accuracy improves, but noise increases in high vibration environments
Solution Approach 1:
The windowed delta-sigma ADC dynamically adjusts its window width parameter based on detected vibration levels. During high vibration periods, the window width is increased to provide noise immunity, while during low vibration periods, the window width is decreased to maximize resolution. This dynamic adjustment resolves the contradiction by adapting the noise tolerance characteristic to match actual environmental conditions.
Solution Approach 2:
The invention modifies the ADC's operational parameters (window width and gain) in response to vibration amplitude. When vibration exceeds a threshold, the window width is expanded and gain is reduced to suppress noise. When vibration is low, the window width is contracted and gain is increased to enhance measurement accuracy. This conditional parameter change eliminates the need to permanently tolerate high noise levels.
3Measurement precision
If the ADC operates in linear mode for high precision, then linearity improves, but the system cannot adapt to varying vibration conditions
Solution Approach 1:
The patent implements a windowed delta-sigma ADC that can dynamically switch between linear and non-linear operational modes. The window width parameter controls the transition: within the window, the ADC operates linearly for high precision; outside the window, it operates non-linearly to handle large excursions and vibrations. This dynamic mode switching resolves the contradiction between maintaining linearity and adapting to varying conditions.
Solution Approach 2:
The invention changes the ADC's transfer function characteristics by adjusting the window width parameter. When vibration is low, a narrow window maintains linear operation for maximum precision. When vibration increases, the window width expands to accommodate non-linear operation, preventing saturation and maintaining adaptability. This parameter-based control enables the system to maintain linearity when needed while adapting to vibration when necessary.
Data Source
AI summary
A data storage device is disclosed comprising a voice coil motor (VCM) configured to actuate a head over a disk. The data storage device further comprises control circuitry comprising a digital current control loop including a windowed delta-sigma analog-to-digital converter (ADC) configured to control the VCM. A vibration of the data storage device is measured, and at least one of a gain or a window of the windowed delta-sigma ADC is configured based on the measured vibration.