Back-EMF Sense System Phase Voltage Measurement
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Solution Overview
Problem
Existing BEMF sense systems in disk-drive systems face challenges in accurately measuring the rotational speed of servo motors due to limitations in selecting and measuring phase voltages relative to center tap voltages, leading to potential errors in rotational speed feedback and control.
Innovation Solution
A BEMF sense system that includes a sense amplifier with selection transistors to decouple and couple control nodes to a voltage source, allowing for the measurement of a selected phase voltage relative to a center tap voltage without introducing additional resistance, thereby enhancing measurement accuracy by isolating the selection process from the signal path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional voltage measurement methods are used to measure phase voltages, then the measurement process is simple, but additional resistance is introduced into the signal path which degrades measurement accuracy
Solution Approach 1:
The sense amplifier circuit is segmented into multiple independent control nodes, each responsible for selecting and measuring a specific phase voltage. This segmentation allows each node to be optimized for high-precision measurement without affecting other phases, thereby improving measurement accuracy while maintaining manageable circuit complexity through modular design.
Solution Approach 2:
Control nodes are introduced as intermediary elements between the voltage source and the measurement system. These control nodes act as isolation points that prevent additional resistance from being introduced into the signal path, thereby maintaining measurement accuracy while still enabling selective phase voltage measurement through the sense amplifier.
2Measurement precision
If phase voltages are measured relative to center tap voltage, then rotational speed can be calculated, but voltage coefficient and temperature coefficient errors affect measurement accuracy
Solution Approach 1:
The sense amplifier incorporates feedback mechanisms that continuously monitor and adjust the measurement process. By using the center tap voltage as a reference and implementing feedback control, the system can compensate for voltage coefficient and temperature coefficient variations, thereby maintaining reliable and accurate rotational speed measurements despite environmental changes.
Solution Approach 2:
The system dynamically adjusts measurement parameters based on detected voltage and temperature conditions. By changing operational parameters such as gain settings and reference voltage levels in response to temperature and voltage variations, the system compensates for coefficient errors and maintains measurement reliability across different operating conditions.
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 precise calculation of BEMF voltage, improving the accuracy of rotational speed monitoring and feedback control of servo motors, reducing errors associated with voltage coefficient and temperature coefficient issues in traditional systems.
Implementation Method 1
monitor a rotational speed of the disk-drive spindle motor, such as by measuring a back electromagnetic force (BEMF) of the servo motor for a given phase of the servo motor. The BEMF of the servo motor can be proportional to the rotational speed of the servo motor
Data Source
AI summary
One embodiment includes a back-electromagnetic force (BEMF) sense system. The system includes a sense amplifier configured to measure an amplitude of a selected one of a plurality of phase voltages relative to a center tap voltage associated with a servo motor for the calculation of an associated BEMF voltage. The plurality of phase voltages can be provided to the sense amplifier via a respective plurality of control nodes. The selected one of the plurality of phase voltages on a respective one of the control nodes can be selected based on coupling the other of the plurality of control nodes associated with the other of the plurality of phase voltages to a voltage source configured to provide a predetermined voltage magnitude.