Spindle Motor Speed Detection via Current Sensing
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Solution Overview
Problem
Conventional disk drive systems face challenges in minimizing contact between read/write heads and magnetic media during spindle motor braking, leading to potential head crashes and damage, especially when the spindle motor is braked before the heads are retracted, and there is a need to determine the spindle motor speed for controlled braking.
Innovation Solution
A circuit comprising a comparator and a motor speed calculation circuit that processes periodic signals indicative of motor speed to determine the spindle motor speed, allowing for controlled braking and minimizing the risk of head crashes by ensuring the spindle motor is braked only when its speed is below a predetermined value, avoiding excessive current that could damage the power stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the spindle motor is braked quickly to minimize head contact time, then productivity is improved, but the risk of head crash increases if the motor is braked before heads are retracted
Solution Approach 1:
The system uses feedback from head position detection to control the braking sequence. The microprocessor monitors head position and only initiates spindle motor braking after confirming heads have reached the parked position, eliminating the risk of head crash while maintaining quick braking performance
Solution Approach 2:
The system performs preliminary head parking action before spindle motor braking. By ensuring heads are retracted to the parking zone first, then braking the spindle motor, the system prevents head crash while achieving minimal head contact time
2Productivity
If the spindle motor is braked before head retraction, then productivity is improved, but object-generated harmful factors increase due to potential head crash damage
Solution Approach 1:
The control system continuously monitors head position and uses this feedback to determine the appropriate timing for spindle motor braking. This ensures braking only occurs after safe head retraction, preventing damage while maintaining fast braking performance
Solution Approach 2:
The system applies preliminary anti-action by preventing spindle motor braking until head position confirms safety. This counteracts the potential harmful effect of premature braking by establishing a safety condition必须先满足
3Device complexity
If spindle motor speed is not accurately detected, then device complexity is reduced, but measurement precision of motor speed is insufficient for controlled braking
Solution Approach 1:
The system uses the existing motor drive circuitry and current sensing capabilities to detect motor speed through back-EMF measurement. This self-service approach utilizes already-present components rather than adding dedicated speed sensors, maintaining low device complexity while achieving sufficient measurement precision for controlled braking
Solution Approach 2:
The existing motor drive circuit is made multi-functional by using it not only for motor control but also for speed detection through current sensing. This universal use of components eliminates the need for separate speed detection hardware, reducing device complexity while providing accurate speed measurement
4Force
If the power stage is subjected to excessive current during braking, then braking force is improved, but the power stage may be damaged
Solution Approach 1:
The braking process is made dynamic and adaptive through closed-loop control. The microprocessor continuously monitors motor speed and adjusts braking current in real-time, increasing current when speed is high for maximum braking force, then reducing current as speed decreases to protect the power stage from excessive current damage
Solution Approach 2:
Feedback from speed detection is used to dynamically control braking current magnitude. The system applies high current only when necessary for effective braking, then reduces current as the motor slows down, preventing power stage damage from sustained excessive current while maintaining strong initial braking force
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
Enables controlled and safe braking of the spindle motor by accurately determining its speed, preventing damage to the power stage and ensuring reliable operation of the disk drive system by minimizing the risk of head crashes and wear on the magnetic media.
Implementation Method 1
a first comparator having input terminals configured to be coupled across a drive transistor adapted to drive a phase of a motor, the first comparator outputting a first periodic signal having a first period indicative of motor speed
Implementation Method 2
In the absence of supply voltage, the spindle motor serves as a voltage generator, the voltage of which depends on its rotational speed and its electric constant
Data Source
AI summary
A circuit includes a comparator having input terminals configured to be coupled across a drive transistor adapted to drive a phase of a motor. The comparator senses a drive current of the motor phase, said sensed drive current represented by a periodic signal whose period is indicative of motor speed. A motor speed calculation circuit receives the periodic signal and processes the periodic signal to determine a speed of the motor.