Iterative Repeatable Runout Nulling for Magnetic Head Testers
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Solution Overview
Problem
The existing head testing devices face challenges in accurately and efficiently writing servo information on magnetic disks due to issues like disk warping, spindle wobble, and thermal shocks, leading to repeatable runout and positioning errors when disks are transferred to different systems, which complicates the head positioning and tracking processes.
Innovation Solution
Pre-writing servo data on dedicated servo disks and using an iterative method to calculate an IRON profile that nullifies repeatable position errors, allowing the head testing device to follow concentric circular tracks with minimal acceleration and error, thereby eliminating the need for servo-writing components within the head tester.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If servo information is written on the disk while the disk is already mounted in the tester using a micro-positioner, then the head can be accurately positioned at target locations, but the device complexity increases and the manufacturing cost increases
Solution Approach 1:
The patent extracts the servo-writing function from the head testing device by using pre-servod disks. The micro-positioner and servo-writing capabilities are removed from the tester, leaving only the essential head testing functionality. This reduces device complexity while maintaining positioning accuracy through the use of pre-written servo information on dedicated servod disks.
Solution Approach 2:
The patent applies preliminary action by pre-writing servo information on disks in a dedicated servo writer before mounting them in the head tester. This eliminates the need for the head tester to have servo-writing capabilities, simplifying the device while ensuring accurate servo tracks are available for head positioning and testing.
2Measurement precision
If the disk is furnished with embedded servo information written by a micro-positioner, then the head positioning accuracy is improved, but the productivity decreases due to the time-consuming writing process
Solution Approach 1:
The patent applies preliminary action by pre-writing servo information on disks in a dedicated servo writer before mounting them in the head tester. This eliminates the need for the head tester to perform time-consuming servo-writing operations, thereby improving testing productivity while maintaining positioning accuracy through the use of pre-established servo tracks.
3Stability of the object's composition
If the actuator is locked at a fixed radial position to follow the target track center line, then the positioning stability is improved, but repeatable runout errors occur due to disk warping and spindle wobble
Solution Approach 1:
The patent applies feedback by using the pre-written servo information to generate position error signals that compensate for repeatable runout errors. The servo tracks are written with precise positioning information that accounts for disk warping and spindle wobble, allowing the head to accurately follow track centers despite physical imperfections. This feedback mechanism maintains both positioning stability and track following accuracy.
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 enhances the accuracy, repeatability, and efficiency of the head testing process by eliminating repeatable runout and other position errors, reducing the cost and time required for testing, and ensuring consistent track spacing and reduced head accelerations.
Implementation Method 1
The VCM, which is a current carrying coil positioned between permanent magnets. The VCM then responds to the DAC generated current and repositions the actuator.
Data Source
AI summary
A method for operating a head testing apparatus or, more generally, a host hard disk drive using a mounted hard disk that has had its servo track information pre-written in an external servo-writing apparatus rather than in the head testing or host apparatus itself. The method eliminates repeatable errors and repeatable runout by effectively replacing the pre-written servo tracks, which are eccentric, with new track profiles that are tracked like circular tracks. The problem of repeatable errors is caused by repeatable runout superimposed upon written-in position errors when a disk written in one machine is transferred to another. This problem is eliminated by forming IRON (Iterative Repeatable Runout Nulling) profile tracks from the initially pre-written servo tracks, where the IRON profile tracks are effectively tracked as concentric circular tracks and generate no PES. The IRON profile is formed by an iterative method that starts with the measurement of the PES of one of the pre-written tracks and iteratively forms a new track profile that is effectively circular.