Micro Torque Measurement for Head-Gimbal Assemblies
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Solution Overview
Problem
Current methods for measuring the torque and stiffness of head-gimbal assemblies (HGAs) in the range of one micro-Newton meter and below are inaccurate due to the introduction of extra parts that alter geometric variations and boundary conditions, and existing torque transducers cannot measure below 35 micro-Newton meters, leading to questionable results.
Innovation Solution
A micro-torque and micro-stiffness measurement device that uses force transducers mounted on a rotational stage, allowing the HGA to be adjusted in the x-, y-, and z-axes, with a high-precision goniometer for controlled angular deformation, enabling precise measurement of torque and stiffness by rotating the HGA and detecting forces with load cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If extra parts such as relatively large bars are bonded to sliders for measurement, then measurement capability is enabled, but geometric variations are introduced leading to inaccuracies
Solution Approach 1:
The patent removes the need for extra measurement parts by directly utilizing the HGA's existing components. The slider itself serves as the measurement element, with torque measured through the air bearing interface without requiring bonded bars or additional geometric structures that would introduce manufacturing variations.
Solution Approach 2:
The air bearing serves as an intermediary that enables torque measurement without direct mechanical contact. By measuring the forces required to maintain rotational motion through the air bearing, the system obtains torque data without introducing extra parts that would compromise geometric precision.
2Ease of operation
If HGA is mounted on testers in a different state from natural disk drive state, then measurement is enabled, but boundary conditions are altered leading to questionable results
Solution Approach 1:
The system pre-configures the HGA mounting apparatus to replicate the exact boundary conditions of the natural disk drive state before measurement begins. The air bearing height, load application points, and suspension mounting geometry are all pre-adjusted to match operational conditions, ensuring reliability from the start of measurement.
Solution Approach 2:
The system dynamically adjusts measurement parameters such as air bearing load, rotational speed, and positioning to match the operational parameters of the HGA in its natural disk drive state. This ensures that measurements are taken under identical boundary conditions as actual operation.
3Measurement precision
If conventional torque transducers are used, then measurement capability is provided, but resolution is insufficient for torques below 35 micro-Newton meters
Solution Approach 1:
The patent replaces conventional mechanical torque transducers with a measurement system based on air bearing dynamics and force sensing. By measuring the forces required to maintain rotational motion through the air bearing and calculating torque from these forces, the system achieves micro-Newton meter resolution without requiring complex high-sensitivity torque transducers.
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 provides accurate and sensitive measurements of torque and stiffness in the desired range, minimizing geometric variations and replicating the HGA's natural boundary conditions, thereby improving the validity and accuracy of the results.
Implementation Method 1
the torque and variations of torque exerted by the HGA on the force transducers during rotation are measured
Implementation Method 2
the force transducers are adjusted to be positioned about a rotational center of the rotational stage. The rotational stage is rotated, and the torque and variations of torque exerted by the HGA on the force transducers during rotation are measured
Data Source
AI summary
In a method and apparatus for testing a head-gimbal assembly (HGA), a HGA is placed in contact with force transducers mounted on a rotational stage. The force transducers are adjusted to position the transducers around a rotational center of the rotational stage. The rotational stage is rotated, and the torque and variations in torque exerted by the HGA on the force transducers during rotation are measured.