Fly Height Sensor Control Circuit for Disk Drive Touchdown Detection
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Solution Overview
Problem
Conventional methods for detecting touchdown events in disk drives lack precision and reliability, as they rely on various indirect techniques such as disk slowdown, noise analysis, and strain gauges, which may not accurately determine the contact between the head and magnetic media.
Innovation Solution
The integration of differential touchdown sensors, specifically thermistors, within the disk drive's head, which measure temperature changes to detect contact through a controlled thermal actuator, allowing for precise detection of touchdown events by comparing the differential voltage and common mode voltage between sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional touchdown detection techniques (disk slowdown, noise analysis, strain gauges) are used, then the detection system is simpler, but the measurement precision and reliability are insufficient
Solution Approach 1:
The patent replaces mechanical detection methods (strain gauges, disk slowdown) with a thermal field-based detection system using thermistors. The thermistors measure temperature changes in the head caused by thermal expansion during touchdown, converting a mechanical contact event into a thermal measurement problem that can be solved with electronic sensing.
Solution Approach 2:
The patent introduces temperature as an intermediary parameter to detect touchdown. Instead of directly measuring mechanical contact or disk motion, the system measures temperature changes in the head that occur during thermal expansion and contact with the disk surface. This intermediary approach enables indirect but precise detection of the touchdown event.
2Manufacturing precision
If thermal actuators are used to control head-media spacing, then the fly height can be controlled, but the thermal expansion during operation may interfere with touchdown detection accuracy
Solution Approach 1:
The patent divides the head into multiple temperature sensing regions by placing separate thermistor sensors at different locations. This segmentation allows the system to distinguish between temperature changes caused by thermal actuator operation (affecting one region) and temperature changes caused by touchdown (affecting the sensor region directly).
Solution Approach 2:
The patent applies local quality by placing thermistor sensors specifically in the region where thermal expansion occurs during touchdown. The sensors are positioned to detect local temperature changes at the critical interface between the head and disk, separating the detection function from the general thermal actuator control function.
3Reliability
If single sensor touchdown detection is used, then the device complexity is lower, but the reliability and accuracy of detection is reduced
Solution Approach 1:
The patent uses asymmetric placement of thermistor sensors at different positions and orientations relative to the head and disk interface. This asymmetric configuration allows the sensors to detect different aspects of thermal expansion and contact events, improving reliability by providing multiple independent measurement perspectives.
Solution Approach 2:
The patent transitions from single-point detection to multi-dimensional temperature field measurement by placing sensors at different spatial locations and potentially different depths or orientations. This dimensional expansion of the measurement system enables more comprehensive detection of touchdown conditions.
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 enables accurate and reliable detection of touchdown events, allowing for precise control of head-media spacing, improving the reliability of disk drive operations and calibration processes.
Implementation Method 1
heads typically use a thermal actuator that generates heat to control the head-media spacing. Heat generated by the thermal actuator causes local thermal expansion of the head
Implementation Method 2
Heat generated by the thermal actuator causes local thermal expansion of the head, which locally reduces the spacing between the head and magnetic media
Implementation Method 3
The integration of differential touchdown sensors, specifically thermistors, within the disk drive's head, which measure temperature changes to detect contact
Data Source
AI summary
A disk drive is disclosed comprising a disk, a head for writing data to the disk, a first touchdown sensor, a second touchdown sensor, and control circuitry comprising a first current source coupled to the first touchdown sensor and a second current source coupled to the second touchdown sensor, the control circuitry operable to determine a common mode voltage between the first touchdown sensor and the second touchdown sensor, adjust the first current source and the second current source until the common mode voltage exceeds a first threshold, determine a differential voltage between the first touchdown sensor and the second touchdown sensor, adjust the first current source and the second current source until the differential voltage exceeds a second threshold, and detect a touchdown event based on the differential voltage exceeding a third threshold.