Stepper Motor Control Circuit for External Magnetic Field Detection
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Solution Overview
Problem
Existing stepper motor control systems for timepieces are complex and inefficient in detecting external magnetic fields, particularly when using pulse-width modulation, making it difficult to manage disturbances and torque variations.
Innovation Solution
An electronic control circuit for stepper motors that detects external magnetic fields by measuring the rise time of electrical current after a pulse, utilizing a bipolar permanent magnet and stator configuration to determine the rotor's position and magnetic flux direction, allowing for detection without pulse-width modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pulse-width modulation is used to control the stepper motor, then the motor can adapt to torque variations and disturbances, but the complexity of detecting external magnetic fields increases significantly
Solution Approach 1:
The patent extracts the magnetic field detection function from the complex PWM control system by using the existing coil and permanent magnet interaction. The detection is achieved by measuring current rise time during normal motor operation, separating the detection function from dedicated sensors while utilizing the motor's inherent electromagnetic components.
Solution Approach 2:
The coil serves dual purposes: it acts as both the actuator for motor operation and the sensor for magnetic field detection. The permanent magnet similarly functions for both motor torque generation and providing a reference magnetic field for detection, eliminating the need for separate dedicated components.
2Power
If pulse-width modulation is used for motor control, then torque control is improved, but the detection method becomes limited to PWM-only applications
Solution Approach 1:
The patent segments the control approach by introducing a specific detection phase within the overall control cycle. During this phase, a test pulse is applied and the current rise time is measured, while other phases maintain normal PWM operation. This segmentation allows the detection method to work independently of the dominant PWM control scheme.
Solution Approach 2:
The patent changes the measurement parameter from pulse width or frequency (PWM characteristics) to current rise time. This parameter change enables magnetic field detection through the natural electromagnetic response of the motor components, making the detection method compatible with various control schemes beyond PWM.
3Manufacturing precision
If the number of electrical pulses per series is increased to compensate for external magnetic field disturbances, then motor step accuracy is maintained, but the maximum duration of pulses must also increase, reducing productivity
Solution Approach 1:
The patent implements feedback by measuring the current rise time and using this information to detect external magnetic field disturbances. Based on this detection, the control system can adjust the number of pulses or pulse duration dynamically, compensating for disturbances while maintaining optimal motor speed and preventing excessive pulse duration extensions.
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
Effectively detects the presence and strength of external magnetic fields with reduced complexity, enabling precise rotor control and minimizing disturbances.
Implementation Method 1
The permanent magnet generates, in the two rest positions, a first magnetic flux passing through the two isthmi respectively in both senses of direction
Implementation Method 2
a coil mounted on the magnetic circuit so as to be able to generate, when supplied with a positive electrical pulse or a negative electrical pulse, a second magnetic flux passing through the two isthmi
Implementation Method 3
a circuit for measuring said electrical current, a circuit for comparing the measured electrical current with a reference current, a time measurement circuit allowing measuring a rise time between triggering of one of said electrical pulses and the next moment in time when the electrical current flowing in the coil reaches the reference current
Data Source
AI summary
A control circuit of a timepiece motor (2), including a bipolar permanent magnet (6), a stator (4) defining two isthmi (12a &12b) and two rest positions for the rotor, and a coil (18) mounted on the stator. The control circuit can determine the position of the rotor at rest. An electric pulse generator (22) for detecting an external magnetic field formed by a circuits for: measuring the electrical current in the coil after an electrical pulse has been triggered, comparing the measured electrical current with a reference current, measuring the time allowing measuring a rise time between triggering of the electrical pulse and the next time the electrical current flowing in the coil reaches the reference current, and processing the rise time to be able to determine whether the measured rise time indicates the presence of a given external magnetic field passing through the two isthmi.