Magnetic Head Retract Control via Dynamic BEMF Skipping
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Solution Overview
Problem
Magnetic disk devices face challenges in efficiently retracting the magnetic head to a target speed during power disconnection or cut-off, leading to potential damage due to high-speed movement, as existing speed feedback control methods are slow and inefficient.
Innovation Solution
The magnetic disk device employs a controller that alternates detection of back electromotive force (BEMF) and application of voltage to the actuator, skipping BEMF detection a predetermined number of times when the magnetic head moves outside a predetermined speed range, allowing for continuous voltage application to rapidly decelerate or accelerate the head to the target speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If speed feedback control is performed by alternating BEMF detection and voltage application, then the magnetic head can be controlled to reach target speed, but the control process takes too long when the magnetic head moves at speed largely different from target speed
Solution Approach 1:
The controller skips BEMF detection for a predetermined number of times when the magnetic head moves at a speed largely different from the target speed. This allows continuous voltage application to the actuator, enabling rapid acceleration or deceleration of the magnetic head to reach the target speed more quickly, thereby resolving the contradiction between speed control accuracy and time to reach target speed.
2Measurement precision
If continuous BEMF detection is performed for speed feedback control, then speed control precision is maintained, but the control response is too slow when rapid speed adjustment is needed
Solution Approach 1:
The controller dynamically adjusts the BEMF detection frequency based on the magnetic head's current speed relative to the target speed. When the speed difference is large, BEMF detection is skipped to enable faster response. When the speed difference is small, normal BEMF detection continues to maintain precision. This dynamic adjustment resolves the contradiction between measurement precision and control response speed.
Solution Approach 2:
The controller changes the detection parameter (BEMF detection frequency) based on the operational state. By skipping detections when rapid adjustment is needed and performing normal detections when precision is needed, the system adapts the measurement frequency to the current control requirements, resolving the contradiction between precision and response speed.
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 the magnetic head to promptly reach and maintain the target speed during retract operations, preventing damage from high-speed movement and reducing the need for additional speed measurement devices, thus enhancing operational safety and efficiency.
Implementation Method 1
the controller is configured to, in a retract operation for causing the actuator to retract the magnetic head to the ramp, alternate detection of a back electromotive force of the actuator and application of a voltage corresponding to the back electromotive force to the actuator
Data Source
AI summary
According to one embodiment, a magnetic disk device includes a magnetic disk, a magnetic head, an actuator, a controller, and a ramp. The magnetic head is configured to record data on and reproduce data from the magnetic disk. The actuator is configured to move the magnetic head relative to the magnetic disk. The controller is configured to control the actuator. The ramp is configured to hold the magnetic head. The controller is configured to, in a retract operation for causing the actuator to retract the magnetic head to the ramp, alternate detection of a back electromotive force of the actuator and application of a voltage corresponding to the back electromotive force to the actuator, and skip the detection of the back electromotive force a predetermined number of times in response to an event that the magnetic head moves at a speed outside a predetermined range.