Pitch and Roll Torque Measurement in HDD VCM
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Solution Overview
Problem
Commercially available three-axis load cells are unable to accurately measure pitch and roll torques in hard disk drive (HDD) voice coil motors due to inadequate resolution and interference from high yaw torques, leading to inaccurate measurements.
Innovation Solution
A device comprising a sensor plate with horizontal and vertical cross members, strain gauges, and a VCM coil that generates pitch and roll torques, along with calibration elements to determine constant values for calculating these torques, minimizing interference from yaw torques and using a Wheatstone bridge circuit for accurate signal measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If commercially available three axis load cells are used to measure pitch and roll torques, then the measurement function is provided, but the resolution is inadequate and yaw torque interference corrupts the pitch and roll torque measurements
Solution Approach 1:
The sensor plate is divided into four independent quadrants, each with its own strain gauge, allowing separate measurement of pitch and roll torque effects. This segmentation enables the system to distinguish between pitch and roll torque contributions without interference from yaw torque, resolving the measurement accuracy problem while maintaining independence from harmful yaw torque factors.
Solution Approach 2:
The sensor plate acts as an intermediary structure between the VCM coil and the strain gauges. It is specifically designed with a semi-rigid structure that is stiff to yaw torque but sensitive to pitch and roll torques, serving as a mediator that isolates the measurement system from yaw torque interference while preserving sensitivity to the target measurements.
2Object-affected harmful factors
If a semi-rigid sensor plate structure is used that is stiff to yaw torque, then yaw torque interference is reduced, but the structure must be carefully designed to maintain sensitivity to pitch and roll torques
Solution Approach 1:
Different regions of the sensor plate are designed with different mechanical properties. The overall plate structure is made semi-rigid to be stiff to yaw torque, while specific local regions (the quadrants with strain gauges) are configured to be sensitive to pitch and roll torques. This local quality differentiation allows the same structure to simultaneously resist yaw torque interference while maintaining sensitivity to target measurements.
Solution Approach 2:
The sensor plate employs asymmetric design in its quadrant configuration and strain gauge placement. The asymmetric arrangement of strain gauges on the four quadrants allows the structure to differentiate between pitch and roll torque directions while maintaining overall stiffness to yaw torque, resolving the design complexity challenge.
3Measurement precision
If strain gauges are attached to cross members to detect strain, then pitch and roll torques can be measured, but the resolution must be adequate to accurately measure small torques
Solution Approach 1:
The patent combines multiple strain gauges on four different quadrants of the sensor plate to measure pitch and roll torques. By merging the signals from multiple strain gauges and using a Wheatstone bridge circuit, the system amplifies the total signal magnitude while maintaining measurement precision for small torques, overcoming the limitation of individual strain gauge signal strength.
Solution Approach 2:
The patent replaces conventional mechanical measurement systems with an electrical measurement system using strain gauges and Wheatstone bridge circuits. This substitution enables more precise measurement of small torques through electrical signal processing, overcoming the resolution limitations of traditional mechanical measurement methods.
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
The solution allows for precise measurement of pitch and roll torques without cross-talk from yaw torques, enhancing the accuracy and reducing fabrication costs through a unique semi-rigid structure that is stiff to yaw but sensitive to pitch and roll torques.
Implementation Method 1
a first strain gauge attached to a surface of the horizontal cross member and configured to detect a horizontal strain caused by the pitch and roll torques generated by the VCM coil; and a second strain gauge attached to a surface of the vertical cross member and configured to detect a vertical strain caused by the pitch and roll torques generated by the VCM coil
Implementation Method 2
each of the first strain gauge and the second strain gauge is wired to a Wheatstone bridge circuit
Implementation Method 3
a VCM coil attached to the sensor plate and configured to generate a pitch torque and a roll torque when an electrical current is applied to the VCM coil
Data Source
AI summary
Embodiments of the invention provide a device for measuring pitch and roll torques. The device comprises a sensor plate having a horizontal cross member, a vertical cross member and a surrounding member connecting ends of the horizontal and vertical cross members, wherein the horizontal cross member and the vertical cross member intersect each other at a centre region of the sensor plate; a VCM coil attached to the sensor plate and configured to generate a pitch and a roll torque when an electrical current is applied to the VCM coil; a first strain gauge attached to a surface of the horizontal cross member and configured to detect a horizontal strain caused by the pitch and roll torques; and a second strain gauge attached to a surface of the vertical cross member and configured to detect a vertical strain caused by the pitch and roll torques.