Dynamic Integrator Range Adjustment for Disk Drive Seek Reliability
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Solution Overview
Problem
In disk drives, uncompensated bias forces on the actuator arm can cause seek operations to fail, leading to timeouts and errors, as existing control circuitry struggles to accurately position the head due to induced bias forces from flex circuits and bearing friction.
Innovation Solution
The output range of an integrator in the servo control system is dynamically adjusted, either by increasing it when errors occur or after a time-limit is reached, to ensure successful seek operations, and additional long seeks are performed when idle to smoothen bias forces, incorporating a proportional/integral compensator and considering vibration states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the integrator output range is limited to prevent windup, then system stability is improved, but the ability to overcome bias forces during seek operations deteriorates
Solution Approach 1:
The integrator output range is made dynamic rather than static. The control circuitry monitors the integrator output and dynamically adjusts the output range limit based on operating conditions. When bias forces are detected or during settle mode, the output range is increased to overcome these forces, while under normal conditions the range is limited to prevent windup. This dynamic adjustment resolves the contradiction by allowing the system to have both stability prevention and bias force overcoming capability at different times.
Solution Approach 2:
The output range parameter of the integrator is changed based on system state. The control circuitry modifies the integrator output range limit parameter from a fixed value to a variable value that changes according to operational conditions. When the head is near the target track and bias forces are present, the parameter is increased; otherwise, it is maintained at a lower level. This parameter change enables the system to adapt to different operational requirements and resolve the contradiction between stability and reliability.
2Reliability
If additional long seeks are performed to smoothen bias forces, then seek operation reliability is improved, but time consumption increases
Solution Approach 1:
Additional long seeks are performed during idle periods to smoothen bias forces before normal seek operations are needed. This preliminary action prepares the actuator arm and flex circuit system for more reliable positioning by reducing bias force variations in advance. By performing these smoothing operations when the system is idle and not under time pressure, the reliability of subsequent seek operations is improved without adding time loss to critical operations.
Solution Approach 2:
The system uses its own idle time to perform maintenance-like operations (smoothing bias forces) without requiring external intervention or dedicated maintenance periods. The actuator arm performs long seeks during naturally occurring idle periods, effectively self-maintaining the system for optimal performance. This self-service approach improves reliability while minimizing additional time consumption since the operations are performed during otherwise unused time.
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 enhances the completion rate of seek operations by preventing integrator windup and overshoot, ensuring accurate head positioning and reducing the likelihood of timeouts, thereby improving the reliability of disk drive operations.
Implementation Method 1
a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk
Implementation Method 2
The output range of an integrator in the servo control system is dynamically adjusted, either by increasing it when errors occur or after a time-limit is reached
Data Source
AI summary
A disk drive is disclosed comprising a disk comprising a plurality of data tracks, a head, and control circuitry comprising a servo control system operable to actuate the head over the disk. When an access command is received to access a target data track, a seek operation is initiated to seek the head toward the target data track, wherein the seek operation includes integrating a first state of the servo control system and limiting an output range of the integrating. The output range of the integrating is increased during the seek operation, for example, if an error occurs during the seek operation.