DC Motor Speed Control Using Frequency-Domain Detection
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Solution Overview
Problem
Existing small electrical appliances, such as hair removal devices and electric toothbrushes, face challenges in maintaining constant DC motor speed under varying load conditions without the need for additional sensors, as motor parameters like winding resistance and manufacturing tolerances can affect control loop accuracy and device-to-device variation.
Innovation Solution
Implementing a controller that performs frequency domain analysis of the detector signal to determine rotational speed parameters independently of motor parameters, allowing for accurate speed control with reduced hardware requirements and manufacturing costs, using a combination of amplitude and frequency domain analysis to adjust the supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional amplitude-based speed control is used, then the control response is fast, but the control accuracy is insufficient due to dependency on motor parameters like winding resistance and manufacturing tolerances
Solution Approach 1:
The patent transitions from one-dimensional amplitude-based speed detection to two-dimensional analysis by incorporating both amplitude and frequency domain information. The frequency domain analysis of the detector signal provides a new dimension that is independent of motor parameters, enabling accurate speed measurement without being affected by winding resistance or manufacturing tolerances
Solution Approach 2:
The patent replaces the traditional mechanical/physical dependency on motor parameters (winding resistance, tolerances) with a signal processing approach. By using frequency domain analysis of electrical signals, the system achieves parameter-independent speed detection, substituting physical measurement dependencies with computational analysis
2Measurement precision
If frequency domain analysis is added to the control system, then the speed control accuracy improves, but the processing requirements and computational load increase
Solution Approach 1:
The patent implements a balanced approach where frequency domain analysis is applied selectively rather than continuously at full computational intensity. The system processes the detector signal in the frequency domain to extract speed information while avoiding excessive computational overhead, achieving sufficient accuracy without requiring maximum processing power
3Reliability
If parameter-independent speed detection is implemented, then the device-to-device variation is reduced, but the manufacturing precision requirements for other components may increase
Solution Approach 1:
The system uses the motor's own operational signals (detector signals from the motor operation) to determine its speed, making the measurement self-contained and independent of external calibration or precise component specifications. The frequency domain analysis extracts speed information directly from the motor's electrical characteristics during operation, eliminating the need for pre-calibration or ultra-precise manufacturing tolerances
Data Source
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AI summary
The present invention relates to the field of small electrical appliances (1, 1') such as battery powered electrical appliances for personal hygiene, in particular to a hair removal device such as an electric shaver or epilator as well as an electric toothbrush. A small electrical appliance (1, 1'), in particular 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 present disclosure further relates to a respective controller and method.