Brushless Motor Speed Control for Low-Speed Hand Tools
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Solution Overview
Problem
Existing technologies fail to provide precise speed control of brushless DC motors, particularly at low speeds, in electric hand-held power tools.
Innovation Solution
The control unit processes Hall interrupts dependent on the angle of rotation and determines actual speed based on time interrupts independent of the angle of rotation, correcting the clock period using offset periods to achieve precise speed determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensor-controlled commutation with Hall sensors is used, then the brushless DC motor can be controlled, but precise speed determination especially at low speeds cannot be achieved
Solution Approach 1:
The speed determination is segmented into two independent components: time interrupts provide the temporal framework (clock period), while Hall interrupts provide the rotational position information. This segmentation allows each interrupt type to be processed independently and combined mathematically, achieving precise speed determination even at low speeds where Hall interrupts alone would be insufficient.
Solution Approach 2:
The control unit acts as an intermediary that processes both time interrupts and Hall interrupts, combining them through mathematical calculation (quotient of Hall interrupts counted in a clock period). This intermediary processing transforms two separate signal types into a unified precise speed measurement, resolving the contradiction between controllability and measurement precision.
2Measurement precision
If Hall interrupts are used for speed determination, then angle of rotation information is available, but timing accuracy is insufficient at low speeds
Solution Approach 1:
Time interrupts generate a periodic clock signal with fixed frequency (e.g., 1 kHz), creating a stable temporal reference frame. Hall interrupts occur periodically based on motor rotation. By counting Hall interrupts within each fixed clock period, the system achieves high timing resolution independent of motor speed, solving the problem of insufficient timing accuracy at low speeds.
Solution Approach 2:
The system uses feedback by continuously monitoring the relationship between Hall interrupts and clock periods, calculating actual speed as the quotient of Hall interrupts counted in a clock period. This feedback mechanism allows real-time speed determination with high accuracy, compensating for timing losses and ensuring precise measurement across all speed ranges.
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
Enables precise speed control of brushless DC motors, especially at low speeds, by accurately calculating the actual speed using Hall and time interrupts, enhancing performance in electric hand-held power tools.
Implementation Method 1
at least one Hall sensor included in the DC motor, the Hall sensor being connected to the switching bridge and set up to detect an angle of rotation of the DC motor
Data Source
AI summary
Electric drive unit with a brushless DC motor and with a switching bridge for sensor-controlled commutation of the DC motor by at least one Hall sensor included in the DC motor, the Hall sensor being connected to the switching bridge and set up to detect an angle of rotation of the DC motor, and the drive unit also having a control unit, which is connected to the switching bridge and by which a setpoint speed for the DC motor can be specified, the control unit being set up to process Hall interrupts that are dependent on the angle of rotation and are caused by the at least one Hall sensor, and to determine an actual speed of the DC motor on the basis of time interrupts that are independent of the angle of rotation and the Hall interrupts that are dependent on the angle of rotation.