HDD Head Touchdown Measurement Optimization
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Solution Overview
Problem
In hard disc drive (HDD) manufacturing, the touchdown measurement method for controlling the flying height of a head over a disk is prone to errors, leading to potential head failure and reduced reliability due to excessive power application, which varies across different heads and disk positions, necessitating precise control and measurement across multiple radial areas.
Innovation Solution
A method for determining a reference value for each disk area through pre-measured data distribution, selecting areas with lower excessive protrusion quantities for initial measurement, and setting limit values to prevent excessive power application, thereby optimizing the measurement order and reducing the risk of head-disk contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If touchdown measurement is executed for each head or each disk writing surface to measure flying height, then measurement precision is improved, but device complexity increases due to the need to divide the disk into multiple radial measurement areas and execute measurements in each area
Solution Approach 1:
The patent applies preliminary action by pre-measuring flying heights at multiple radial positions before the actual touchdown measurement process. These pre-measured values are stored and used to determine the measurement order, allowing the system to plan the measurement sequence in advance rather than executing measurements randomly or sequentially without optimization. This reduces the complexity of real-time decision-making during the measurement process.
Solution Approach 2:
The patent changes the parameter of measurement order based on pre-measured flying height data. By calculating excessive protrusion quantities from pre-measured values and using these to determine an optimal measurement sequence, the system adapts the measurement parameters dynamically. This allows prioritization of areas with lower excessive protrusion, improving measurement efficiency while maintaining precision.
2Measurement precision
If power is applied to the heating element to thermally expand the head for touchdown measurement, then measurement capability is improved, but reliability deteriorates due to potential head contact with the disk when power exceeds the real value
Solution Approach 1:
The patent applies preliminary action by pre-measuring flying heights at multiple radial positions and storing these values. These pre-measured data are used to calculate excessive protrusion quantities and determine a safe measurement order before actual touchdown measurements are performed. This preliminary preparation allows the system to anticipate potential risks and plan measurements that minimize the chance of excessive power application and head-disk contact.
Solution Approach 2:
The patent uses feedback by utilizing pre-measured flying height data to inform and adjust the subsequent touchdown measurement process. The pre-measured values provide feedback about the disk surface characteristics and head flying behavior, allowing the system to adjust measurement parameters and power application levels to stay within safe limits and prevent head contact with the disk.
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 reliability and performance of HDDs by minimizing excessive protrusion and preventing abnormal flying heights during read/write operations, thus improving the overall reliability and efficiency of the magnetic disk device.
Implementation Method 1
a touchdown measurement is known as one process for controlling a gap (the flying height of a head) between a head and a disk. The touchdown measurement is a method of applying power to the heating element (heater) of a head to thermally expand part of the head so as to protrude it to a disk
Data Source
AI summary
According to one embodiment, a measurement method is applied to a disk device including a disk, and a head configured to protrude toward the disk when power is supplied thereto. In the method, a reference value for each of areas of the disk is acquired from a measurement-value distribution including pre-measured values that correspond to power supplied to a heater when the head is brought into contact with the disk. In each area, a data group calculated from the distribution and the reference value is acquired. An area where the data group has lower values than in the other areas is selected as a first area to be firstly measured. An area to be measured subsequent to the first area based on the data group is selected.