Back-EMF Motor Speed Control for Small Electric Appliances
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Solution Overview
Problem
Existing controllers for small electrical appliances like hair removal devices and toothbrushes struggle to maintain constant motor speed under varying load conditions without requiring additional sensors, leading to reduced performance and manufacturing cost inefficiencies.
Innovation Solution
A controller that uses frequency domain analysis of detector signals to determine two parameters indicative of motor speed, allowing for both coarse and fine adjustments to the supply voltage, enabling high-accuracy speed control without additional sensors and reducing manufacturing costs by relaxing hardware tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional speed control methods are used without additional sensors, then manufacturing costs are reduced, but motor speed control accuracy deteriorates under varying load conditions
Solution Approach 1:
The system uses the motor's own back-EMF signal for speed estimation without requiring external sensors. The back-EMF detector captures the natural electrical signal generated by the motor during operation, and the controller processes this signal to determine rotational speed, allowing the motor to serve its own measurement needs
Solution Approach 2:
The system estimates motor speed by analyzing changes in electrical parameters (back-EMF voltage) rather than directly measuring mechanical rotation. By monitoring the back-EMF signal characteristics and processing them through the controller, the system derives speed information from electrical parameter variations
2Measurement precision
If sensor-based speed control is implemented, then motor speed control accuracy is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The controller performs multiple functions: it not only controls motor operation but also detects back-EMF signals and estimates rotational speed. This multi-functionality eliminates the need for separate speed sensors, reducing device complexity while maintaining control accuracy
Solution Approach 2:
The speed detection and control functions are merged into a single integrated controller system. The controller simultaneously manages power delivery to the motor and processes back-EMF signals for speed estimation, combining what would traditionally be separate components
3Stability of the object's composition
If fast control response is implemented for varying loads, then motor speed stability is improved, but processing requirements and complexity increase
Solution Approach 1:
The system continuously monitors the back-EMF signal and uses this feedback to adjust motor control in real-time. The controller compares the estimated speed from back-EMF analysis with the desired speed and modifies power delivery accordingly, creating a closed-loop control system that maintains speed stability under varying loads
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 provides accurate motor speed control across varying loads with reduced manufacturing costs, allowing for flexible implementation and improved performance even in devices with limited processing power, while minimizing the need for dedicated 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
Data Source
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AI summary
The present invention relates to a small electrical appliance (1, 1'), wherein the small electrical appliance (1) is a hair removal device (1), such as an electric shaver or epilator, or an electric toothbrush (1'). A small electrical appliance (1, 1'), being a hair removal device (1) or toothbrush (1'), is provided comprising an electric DC motor (5); a detector (10) for acquiring a detector signal indicative of a rotational speed of the electric DC motor (5); and a controller (20) for controlling the electric DC motor (5). The controller is adapted to: determine, based on the detector signal, a first parameter indicative of the rotational speed of the DC motor (5); determine, based on the detector signal, a second parameter indicative of the rotational speed of the DC motor (5), 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 (5) based on the first parameter and the second parameter. The controller (20) is adapted to perform coarse control for adjusting the supply voltage based on the first parameter and to perform fine control for adjusting the supply voltage based on the second parameter. The present disclosure further relates to a corresponding method.