Stepping Motor Back-EMF Detection via PWM Halt
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing out-of-step detection methods for stepping motors face challenges in accurately measuring back electromotive voltage due to noise interference from pulse width modulation (PWM) voltage switching, leading to erroneous detection.
Innovation Solution
A motor control device and method that applies pulse voltage with PWM to phase coils of a stepping motor, temporarily halts voltage application to one coil during current direction switch, measures back electromotive voltage during this halt, and sets other coils to a constant voltage level, preventing noise interference and enabling accurate out-of-step detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If pulse width modulation (PWM) is used to control voltage application to phase coils, then motor control precision is improved, but noise is generated during voltage switching that interferes with back electromotive voltage measurement
Solution Approach 1:
The patent extracts the measurement function from the continuous PWM control process by temporarily halting voltage application to the target phase coil during a specific time period. This separation allows the back electromotive voltage to be measured without superimposed PWM switching noise, while the other phase coils continue to receive PWM control signals to maintain motor operation.
Solution Approach 2:
The patent implements periodic measurement cycles where the voltage application to each phase coil is temporarily halted at regular intervals to measure back electromotive voltage. This periodic halting is synchronized with the motor's rotation cycle, ensuring accurate measurements are taken at optimal moments while maintaining continuous motor control through the other phases.
2Measurement precision
If voltage application to a phase coil is halted for back electromotive voltage measurement, then measurement accuracy is improved, but motor torque may be affected
Solution Approach 1:
The patent applies periodic halting of voltage application to each phase coil in a cyclic manner, where one phase is halted for measurement while other phases continue to provide torque. This periodic measurement approach ensures that the motor receives sufficient torque from the active phases while still allowing accurate back electromotive voltage measurements to be taken from the halted phase.
Solution Approach 2:
The patent merges the measurement function with the control function by coordinating the halting of voltage application with the motor's rotation cycle. The measurement is performed during the natural commutation period when the phase current is already transitioning, thereby minimizing the impact on motor torque while enabling accurate back electromotive voltage measurement.
3Duration of action of stationary object
If back electromotive voltage is measured during PWM voltage application, then continuous motor control is maintained, but noise from voltage switching is superimposed on the measurement waveform
Solution Approach 1:
The patent extracts the measurement function from the continuous PWM control process by temporarily halting voltage application to the target phase coil during a specific time period. This separation allows the back electromotive voltage to be measured without superimposed PWM switching noise, while the other phase coils continue to receive PWM control signals to maintain motor operation.
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 precise detection of out-of-step conditions in stepping motors, reducing erroneous readings and improving detection accuracy.
Implementation Method 1
measures a back electromotive voltage induced in the one phase coil during the halt period
Data Source
AI summary
A motor control device for a stepping motor including at least two phase coils and a rotor is provided. The motor control device includes a control unit which applies a pulse voltage subjected to pulse width modulation, to each of the at least two phase coils, a back electromotive voltage measuring unit which provides a halt period to temporarily halt the application of the pulse voltage to one of the phase coils when a direction of the coil current flowing in the one phase coil is switched, and which measures a back electromotive voltage induced in the one phase coil during the halt period, an out-of-step detecting unit which detects an out-of-step of the stepping motor if the measured back electromotive voltage satisfies a predetermined criterion, and a voltage control unit which sets a voltage for all phase coils other than the one phase coil to a constant voltage during the halt period.