DC Motor Speed Control Using Back-EMF and Frequency Analysis
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Solution Overview
Problem
Existing hair removal devices, such as electric shavers and epilators, face challenges in maintaining constant motor speed under varying load conditions without the need for additional sensors, which can affect manufacturing costs and device performance.
Innovation Solution
A controller system for a DC motor in hair removal devices that uses a detector to acquire a signal indicative of rotational speed, determining two parameters - one based on amplitude and the other on frequency domain analysis - to adjust the supply voltage, allowing for both fast and precise control of motor speed without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single control parameter is used to adjust motor speed, then the control system is simple, but the speed control accuracy under varying load conditions deteriorates
Solution Approach 1:
The control parameter is segmented into two distinct parameters: a first control parameter for fast response and a second control parameter for high precision. The controller selectively applies different parameters based on operational requirements, achieving both speed and accuracy without requiring a completely complex system architecture.
Solution Approach 2:
The control system dynamically switches between different control parameters based on real-time conditions. The controller determines whether to use the first control parameter or the second control parameter based on the current operational state, enabling adaptive optimization of both response speed and control precision.
2Measurement precision
If additional rotation sensors are added to improve speed control accuracy, then the measurement precision improves, but the manufacturing cost and device complexity increase
Solution Approach 1:
The motor itself generates the signal needed for speed measurement through its back electromotive force (BEMF). The control system utilizes this self-generated signal from the motor's own operation, eliminating the need for external rotation sensors and reducing manufacturing costs while maintaining measurement precision.
Solution Approach 2:
The existing motor windings serve dual purposes: they function as both the actuator that drives the rotor and as the sensor that provides speed feedback through BEMF measurement. This multi-functionality eliminates the need for separate sensing components, reducing device complexity and manufacturing cost.
3Productivity
If fast control response is prioritized, then the productivity improves, but the control precision deteriorates
Solution Approach 1:
The control parameter is segmented into two distinct parameters: a first control parameter for fast response and a second control parameter for high precision. The controller selectively applies different parameters based on operational requirements, achieving both speed and accuracy without requiring a completely complex system architecture.
Solution Approach 2:
The control system dynamically switches between different control parameters based on real-time conditions. The controller determines whether to use the first control parameter or the second control parameter based on the current operational state, enabling adaptive optimization of both response speed and control precision.
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
The solution enables high-accuracy control of motor speed across varying load conditions, reducing device-to-device variation and manufacturing costs, while maintaining performance without the need for dedicated rotation sensors.
Implementation Method 1
Once the motor constant is calibrated, it transitions to back electromotive force (BEMF) measurement method for operation
Implementation Method 2
determine, based on the detector signal, a second parameter indicative of the rotational speed of the DC motor, wherein the second parameter is different from the first parameter, and wherein the second parameter is determined based on a frequency domain analysis (spectral analysis) of the detector signal
Data Source
AI summary
The present invention relates to the field of a small electrical appliance, in particular hair removal device or toothbrush, comprising an electric DC motor; a detector for acquiring a detector signal indicative of a rotational speed of the electric DC motor; and a controller for controlling the electric DC motor. The controller is adapted to: determine, based on the detector signal, a first parameter indicative of the rotational speed of the DC motor; determine, based on the detector signal, a second parameter indicative of the rotational speed of the DC motor, wherein the second parameter is different from the first parameter, and wherein the second parameter is determined based on a frequency domain analysis of the detector signal; and adjust a supply voltage of the electric DC motor based on the first parameter and the second parameter.