Spindle Motor Current Sensor Calibration for Fabrication Tolerance Compensation
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Solution Overview
Problem
Existing data storage devices face inaccuracies in head positioning due to fabrication tolerances and thermal responses, affecting the accuracy of current sensing measurements in spindle motor drivers, which impact the precision of servo control systems.
Innovation Solution
The implementation of a compensation value calibration system that adjusts current sensors to account for fabrication tolerances and thermal responses, using calibration currents to simulate normal operating modes and optimize current measurements, thereby improving the accuracy of relative current sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensors are used to measure spindle motor current, then head positioning control can be achieved, but fabrication tolerances cause measurement inaccuracies
Solution Approach 1:
The system performs preliminary calibration by measuring actual current values during manufacturing or initialization and storing compensation values before normal operation begins. These pre-determined compensation values are then applied during runtime to correct measurement errors caused by fabrication tolerances in the current sensors.
Solution Approach 2:
The system changes the operational parameters of the current sensors by applying compensation values that adjust their measurement characteristics. This allows the sensors to operate within their tolerance ranges while producing accurate readings through parameter adjustment rather than requiring perfect manufacturing precision.
2Measurement precision
If calibration currents are applied to compensate for fabrication tolerances, then measurement accuracy improves, but additional control circuitry and calibration steps are required
Solution Approach 1:
The calibration functionality is merged with the existing current sensor circuitry and control system. The same control circuit that drives the spindle motor also performs calibration by injecting test currents and measuring responses, eliminating the need for separate calibration hardware and reducing overall device complexity.
Solution Approach 2:
The control circuitry is designed to perform multiple functions: normal spindle motor control, current sensing, calibration current injection, and compensation value storage. This multi-functionality reduces the need for dedicated calibration hardware and simplifies the overall system architecture.
3Measurement precision
If thermal response compensation is implemented, then head positioning precision improves, but measurement and control complexity increases
Solution Approach 1:
The system implements thermal compensation by continuously monitoring current measurements and comparing them against expected values that account for thermal effects. The difference is fed back as a compensation value that adjusts subsequent measurements, creating a closed-loop system that automatically corrects for thermal drift without requiring complex external measurement equipment.
Data Source
AI summary
A data storage device is disclosed comprising a spindle motor configured to rotate a disk, wherein the spindle motor comprises a stator, a rotor, and a plurality of windings. The data storage device further comprises an isolation circuit configured to isolate the windings from a supply voltage, a head actuated over the disk, and control circuitry comprising a spindle motor driver comprising a plurality of switches including a first switch and a second switch configured to commutate the windings. While driving the isolation circuit with a first calibration current, the first switch is driven with a second calibration current and a first current flowing through the first switch is measured. While driving the isolation circuit with the first calibration current, the second switch is driven with the second calibration current and a second current flowing through the second switch is measured.