Smart Braking for Voice Coil Motors Using Back-EMF Voltage
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Solution Overview
Problem
Existing data storage devices face challenges in safely unloading heads during power failures, as the braking power generated by back electromotive force (BEMF) voltage may not be sufficient to prevent head damage from contacting disk ramps at high velocities, especially when heads are near the outer diameter of the disk.
Innovation Solution
The solution involves applying a variable brake voltage based on the initial velocity and position of each voice coil motor (VCM) during a power failure, using a non-inverting and inverting amplifier system to generate differential brake voltages, and employing a lookup table to determine optimal brake voltages and intervals to ensure safe unloading without exceeding current limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If back electromotive force (BEMF) voltage is used for braking during power failure, then energy recovery is achieved, but braking power is insufficient to prevent head damage at high velocities
Solution Approach 1:
The patent combines the BEMF voltage from the spindle motor with an external power source to create a hybrid braking system. The control circuitry rectifies and combines these voltage sources to generate higher brake voltages that can effectively stop VCMs at high velocities while still recovering energy through the BEMF pathway.
Solution Approach 2:
The braking system dynamically adjusts the brake voltage applied to each VCM based on real-time monitoring of VCM velocity and position. The control circuitry modifies braking parameters during the braking process to optimize both energy recovery and braking effectiveness under varying operational conditions.
2Reliability
If higher brake voltage is applied to increase braking power, then head safety is improved, but current limits of the BEMF voltage are exceeded
Solution Approach 1:
The patent merges the BEMF voltage with voltage from an external power source to create a combined voltage source. This combination provides sufficient current and voltage to achieve effective braking without overloading the BEMF voltage, as the external source supplements the available power.
Solution Approach 2:
The control circuitry acts as an intermediary that manages power distribution from multiple sources. It rectifies, regulates, and allocates power from both the BEMF voltage and external source to each VCM, ensuring current limits are not exceeded while providing adequate braking power.
3Measurement precision
If variable brake voltage is applied to each VCM based on velocity and position, then braking precision is improved, but control system complexity increases
Solution Approach 1:
The control circuitry pre-calculates and stores optimal braking parameters for different VCM velocities and positions. During braking, the system simply retrieves and applies the appropriate pre-determined parameters, achieving precise control without requiring complex real-time calculations for each VCM.
Solution Approach 2:
The braking control is segmented into discrete velocity and position ranges, each with predetermined brake voltage parameters. This segmentation allows the complex control problem to be divided into manageable segments that can be handled through lookup tables or simplified control logic.
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 effectively reduces the frequency of head-ramp contacts at excessive velocities, minimizing damage by applying more braking power when necessary, thereby ensuring safer and more reliable head unloading during power failures.
Implementation Method 1
the braking power generated by back electromotive force (BEMF) voltage
Data Source
AI summary
A data storage device is disclosed comprising a first voice coil motor (VCM) comprising a first voice coil, and a second VCM comprising a second voice coil. The first VCM and the second VCM are unloaded during a power failure by measuring a first velocity and a first position of the first VCM and measuring a second velocity and a second position of the second VCM. A BEMF voltage generated by a spindle motor is used to generate a first brake voltage based on the first velocity and the first position, and the BEMF voltage is used to generate a second brake voltage based on the second velocity and the second position. The first brake voltage is applied to the first voice coil, and the second brake voltage is applied to the second voice coil.