Brushless Power Tool Commutation Control to Prevent Motor Reversal
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Solution Overview
Problem
Cordless power tools driven by conventional brushed motors face issues with durability, energy efficiency, and electronic control challenges, particularly in maintaining proper commutation and electronic braking, which affect their performance and longevity.
Innovation Solution
A power tool equipped with a brushless DC motor and a control unit that utilizes a Hall Effect sensor to manage commutation electronically, incorporating a variable-speed actuator and a microcontroller to prevent inadvertent motor reversal and implement efficient electronic braking through a delay mechanism and shared MOSFET braking current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a brushless DC motor with electronic commutation is used, then durability and energy efficiency are improved, but device complexity increases due to the need for control circuits and sensors
Solution Approach 1:
The patent extracts the mechanical commutation function from the motor structure and relocates it to an electronic control system. The mechanical commutator and brushes are completely removed, and their function is replaced by electronic switching of stator windings controlled by a microcontroller, thereby improving durability while managing complexity through functional relocation
Solution Approach 2:
The patent replaces the mechanical commutation system with an electronic commutation system. The mechanical brushes and commutator are substituted by electronic switches (MOSFETs or IGBTs) controlled by a microcontroller, eliminating mechanical wear while achieving the same commutation function through electrical means
2Loss of substance
If electronic braking is implemented in a brushless motor, then mechanical wear is reduced, but control complexity increases and timing synchronization becomes challenging
Solution Approach 1:
The patent implements preliminary action by maintaining the controller in a standby state with power supplied during the braking period. The controller pre-prepares the braking sequence and executes it immediately when the trigger is released, ensuring proper timing and synchronization of the electronic braking operation before the motor comes to a complete stop
Solution Approach 2:
The patent uses feedback from Hall effect sensors that continuously monitor rotor position and provide real-time information to the microcontroller. This feedback mechanism enables the controller to precisely synchronize the electronic braking action with the rotor's angular position, ensuring effective braking while managing control complexity through closed-loop control
3Speed
If angle advancing is used to improve motor response, then speed performance is enhanced, but motor reversal becomes more likely at low speeds
Solution Approach 1:
The patent implements dynamics by making the angle advancing parameter variable rather than fixed. The microcontroller dynamically adjusts the angle advancing value based on the motor's operating conditions, particularly reducing or eliminating angle advancing when the motor operates at low speeds or during startup, thereby preventing motor reversal while maintaining speed performance at higher operating speeds
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 enhances the durability and energy efficiency of cordless power tools by minimizing mechanical wear, improving commutation reliability, and ensuring smooth electronic braking, thereby extending tool operation time and reducing heat generation.
Implementation Method 1
A set of sense magnets coupled to the PMs in the rotor assembly are sensed by a sensor, such as a Hall Effect sensor, to identify the current position of the rotor assembly.
Implementation Method 2
When power is applied to a winding, the resulting current in the winding generates a magnetic field that couples to the rotor. The magnetic field associated with the PM in the rotor assembly attempts to align itself with the stator generated magnetic field resulting in rotational movement of the rotor.
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A power tool includes a brushless DC motor housed inside a tool housing, an input unit, and a control unit. The motor includes a rotor, a stator, and at least one sensor positioned to sense a state of the rotational position of the rotor inside the stator. A control unit controls commutation of the motor through a series of power switches coupled to the power supply. The control unit receives a current sensor state from the sensor and a user-selected speed from the input unit and determines whether the motor has reversed direction using the user-selected speed and the current sensor state. The control unit disables commutation of the motor if the motor has reversed direction until a proper current sensor state is received from the sensor.