Stepping Motor Out-of-Step Detection Using PWM Stop Period
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Solution Overview
Problem
Existing techniques for detecting out-of-step in stepping motors, such as those described in EP 1460757 A1 and JP-A-2009-261045, face challenges in accurately measuring back electromotive voltage due to noise from pulse width modulation (PWM) and result in erroneous detection, while methods like JP-A-2012-016221 complicate motor control by switching to constant voltage control.
Innovation Solution
A motor control device with a controller that applies pulse width modulation to coils, provides a stop period for measuring back electromotive voltage, and sets the on-duty of pulse voltage for all coils except the target coil to either 100% or 0% during the stop period, allowing precise detection of out-of-step conditions without noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pulse width modulation is applied to coils during back electromotive voltage measurement, then motor control efficiency is maintained, but measurement precision deteriorates due to noise interference
Solution Approach 1:
The control period is segmented into a drive period with PWM control and a measurement period with voltage control. This temporal segmentation allows PWM to be applied during drive operations for efficient motor control while being suspended during measurement operations for accurate back electromotive voltage detection, thereby resolving the contradiction between maintaining motor control efficiency and achieving measurement precision.
2Measurement precision
If constant voltage control is switched to during measurement period, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The control device dynamically switches between PWM control mode and voltage control mode based on the operational phase. During the drive period, PWM control is active for efficient motor operation; during the measurement period, voltage control is activated for accurate measurement. This dynamic adaptation allows the system to maintain high measurement precision while avoiding permanent complexity increases, as the control mode is flexibly adjusted based on real-time needs.
3Power
If PWM control is continuously applied to all coils, then motor performance is maintained, but harmful noise factors increase during measurement
Solution Approach 1:
The harmful PWM noise is extracted and removed from the measurement period. The control device identifies the measurement period and suspends PWM control specifically during this time, extracting the noise factor from the system when it would otherwise interfere with measurement. This selective removal of PWM control during measurement while maintaining it during drive operations resolves the contradiction between maintaining motor performance and eliminating noise interference.
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 high-precision detection of out-of-step conditions in stepping motors using a simple control method, preventing erroneous detection and maintaining efficient motor control.
Implementation Method 1
measuring a back electromotive voltage induced in a coil during the stop period
Data Source
AI summary
There is provided a motor control device for controlling a stepping motor having at least two coils. The motor control device includes a controller applies a pulse voltage being subjected to pulse width modulation to each of the coils and provides a stop period to a target coil being subjected to switching of a direction of the coil current, during which the application of the pulse voltage to the target coil is temporarily stopped. The controller also performs a control to set on-duty of the pulse voltage applied to all of the coils except the target coil to be either 100% or 0% during the stop period. An out-of step of the stepping motor is detected when a back electromotive voltage induced in the target coil during the stop period satisfies a predetermined out-of-step determination criterion.