Back-EMF Phase Detection in Stepper Motors Using PWM Period Differences
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Stepper motors driven by constant-current PWM face challenges in detecting back electromotive force phase without additional detectors, leading to potential synchronization loss and increased costs and failure factors.
Innovation Solution
A method and device for detecting the back electromotive force phase in a two-phase excitation stepper motor using timing signals and difference calculations between PWM control periods to adjust drive current and prevent synchronization loss, without the need for additional detectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a detector is attached to the motor to detect back electromotive force phase, then detection accuracy is improved, but cost increases and the number of parts increases
Solution Approach 1:
The motor controller uses its existing internal resources (CPU, timers, PWM control circuits) to detect the back electromotive force phase by analyzing the voltage across the motor coil during PWM off-periods, eliminating the need for external detectors. The system serves itself by utilizing components already present in the control circuitry.
Solution Approach 2:
The motor controller performs multiple functions using the same hardware components: it controls motor drive current through PWM switching, detects back electromotive force phase by sampling voltage during off-periods, and adjusts excitation timing based on detection results. This multi-functionality eliminates the need for dedicated detection hardware.
2Reliability
If excessive drive current is supplied to secure sufficient drive torque margin, then reliability is improved, but power consumption increases
Solution Approach 1:
The system dynamically adjusts the drive current and excitation timing based on real-time back electromotive force phase detection. Instead of supplying excessive current continuously, the controller optimizes the current magnitude and timing according to the detected phase, maintaining sufficient torque margin only when needed while reducing power consumption during normal operation.
Solution Approach 2:
The system implements feedback control by detecting the back electromotive force phase and using this information to adjust the drive current and excitation timing. This closed-loop approach ensures reliable synchronization maintenance while avoiding excessive power consumption by supplying current only at optimal moments and magnitudes.
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 allows for effective detection and adjustment of the back electromotive force phase, preventing stepper motor synchronization loss and reducing costs by eliminating the need for additional detectors, thereby optimizing power consumption and motor performance.
Implementation Method 1
a back electromotive force phase detecting device for detecting a back electromotive force phase of a motor coil
Data Source
AI summary
In a back electromotive force phase detecting device, a timing generating unit generates a timing signal indicating a start timing, an intermediate timing and an end timing of a 180-degree electrical angle period in a detection target phase, from an excitation pulse signal. A difference calculating unit receives the timing signal, and calculates a difference between a total PWM control period of the detection target phase during a first-half 90-degree period, and a total PWM control period of the detection target phase during a second-half 90-degree period. In an excitation control device, a control unit changes the capability of driving a motor based on an output of the back electromotive force phase detecting device.