Disk Drive Self-Servo Writing Clock Compensation
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Solution Overview
Problem
The high cost and requirement for a clean room environment of external servo writers for writing concentric servo sectors in disk drives make them a bottleneck in manufacturing, prompting the need for a more efficient and cost-effective method.
Innovation Solution
The use of external spiral servo writers to create spiral tracks on a disk, which are then processed to write product servo sectors using a self-servo writing method, involving synchronization of a servo write clock and compensation for radial dependent phase errors to ensure accurate and even spacing of servo sectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If external servo writers are used to write concentric servo sectors, then manufacturing precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent implements self-servo writing where the disk drive's internal servo system writes the concentric servo sectors to its own disk without requiring external servo writers. The servo controller generates servo bursts and position error signals to position the read/write head and write the servo sectors, enabling the system to service itself and eliminate complex external positioning equipment.
Solution Approach 2:
The patent replaces the mechanical positioning system of external servo writers (which use physical pins and mechanical actuators for precise head positioning) with an electronic control system. The servo controller uses electronic signals, phase-locked loops, and digital processing to achieve the same positioning function, substituting mechanical complexity with electronic control.
2Manufacturing precision
If external servo writers are used to write concentric servo sectors, then manufacturing precision is improved, but ease of manufacture deteriorates
Solution Approach 1:
The disk drive performs self-servo writing using its own internal servo controller and read/write head, eliminating the need for separate external servo writing equipment. This integrates the servo sector writing function into the normal disk drive manufacturing flow, making the process simpler and more self-contained.
Solution Approach 2:
The patent makes the read/write head and servo controller perform multiple functions: they are used both for normal data operations and for writing the concentric servo sectors. This multi-functionality eliminates the need for dedicated external servo writing equipment, simplifying the manufacturing process.
3Manufacturing precision
If external servo writers are used to write concentric servo sectors, then manufacturing precision is improved, but productivity deteriorates
Solution Approach 1:
The self-servo writing process allows disk drives to be manufactured without requiring clean room environments and complex external positioning equipment. This simplifies the manufacturing setup and enables higher production volumes, as the process can be performed in more flexible environments and with simpler equipment.
Solution Approach 2:
The patent extracts the servo sector writing function from the complex external servo writer system and integrates it into the disk drive's own servo controller. This removes the bottleneck of external equipment availability and allows continuous manufacturing without waiting for external servo writing resources.
4Ease of manufacture
If self-servo writing is used to write concentric servo sectors, then ease of manufacture is improved, but manufacturing precision deteriorates
Solution Approach 1:
The patent employs feedback mechanisms where the servo controller continuously monitors the head position using detected servo bursts from previously written sectors, generates position error signals, and adjusts the head positioning in real-time during the self-servo writing process. This closed-loop control ensures high positioning accuracy despite the simplified manufacturing process.
Solution Approach 2:
The patent uses preliminary actions such as writing spiral servo tracks first, then using those as a reference for writing the final concentric servo sectors. Phase-locked loops are used to pre-synchronize the writing clock to the disk rotation before actual servo sector writing begins, ensuring accurate timing and positioning from the start of the process.
Data Source
AI summary
A disk drive is disclosed comprising a disk comprising servo data, and a head actuated over the disk. An offset r0 representing a difference between an axial rotation of the disk and an axial rotation of the servo data is estimated, and radial dependent timing compensation values are generated in response to the estimated r0. A phase error is generated in response to the servo data, and a control signal is generated in response to the phase error and the radial dependent timing compensation values. A frequency of an oscillator is adjusted in response to the control signal.