Brushless Motor Lock Detection via PWM and Current Thresholds
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Solution Overview
Problem
Electric rotating tools, such as driver drills, experience reduced operating efficiency and risk of motor burnout due to rapid temperature increases when the load exceeds the allowable torque, leading to locked states and excessive current flow in brushless DC motors.
Innovation Solution
An electric rotating tool with a lock state detection system that includes a current detection part, rotation number detection part, and control part to generate PWM signals, which detect and manage locked states by adjusting threshold values, restricting drive current, and implementing motor stopping mechanisms to prevent burnout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the load in cutting operation becomes equal to or larger than allowable torque of the electric motor, then the electric motor generates sufficient power, but the electric motor enters locked state causing rapid temperature increase and potential burnout
Solution Approach 1:
The control part detects the locked state of the motor before actual damage occurs by monitoring rotation number and current, and executes protective stopping action in advance to prevent temperature increase and burnout
Solution Approach 2:
The system continuously monitors motor rotation number and current, compares them against threshold values, and provides feedback to the control part to determine locked state and trigger protective measures
2Temperature
If the electric motor is stopped to cool down after locked state, then the temperature increase is prevented, but the fastening operation or cutting operation has to be temporarily stopped reducing operating efficiency
Solution Approach 1:
The control part detects the locked state and executes protective stopping before temperature reaches dangerous levels, preventing the need for extended cooling periods and minimizing operational interruption
Solution Approach 2:
The system automatically detects locked state and executes protective stopping without operator intervention, and can automatically resume operation after protective stopping, reducing downtime and maintaining productivity
3Reliability
If threshold values for lock detection are set low, then locked state is detected early preventing damage, but normal operation may be interrupted due to false detection
Solution Approach 1:
The system uses multiple parameters (rotation number and current) with specific threshold values to detect locked state, balancing early detection with avoidance of false positives during normal operation
Solution Approach 2:
The control part continuously monitors both rotation number and current, comparing against threshold values to determine locked state, providing feedback that distinguishes actual locked states from normal high-load operation
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
Accurate detection and management of locked states prevent motor burnout, enhance operating efficiency, and allow continuous operation without interrupting tasks, improving battery life per charge.
Implementation Method 1
a control part which generates and outputs a PWM signal for driving the semiconductor switching element of the inverter circuit part
Implementation Method 2
a current detection part which detects a drive current, which flows through the stator coil, and outputs a signal corresponding to a result of the detection
Implementation Method 3
a rotation number detection part which detects the number of rotations of the rotor and outputs a signal corresponding to a result of the detection
Implementation Method 4
an inverter circuit part which has a semiconductor switching element inserted between the power source part and the stator coil
Data Source
AI summary
A current detection circuit (18) detects that a drive current of the stator coil (2d) is exceeding a threshold value Ir. A rotation number detection circuit (17) detects that the number of rotations of a rotor (2a) is lower than a threshold value Nr. A computing part (20) outputs a PWM signal which switches a semiconductor switching element (3a) of the inverter circuit part (3). The computing part (20) changes the threshold values Ir and Nr in accordance with the PWM duty of the PWM signal determined in accordance with a pressed distance of a switch trigger (7) and detects a locked state of the motor (2) on the conditions that the motor current I is exceeding the set threshold value Ir and that the number of rotations N thereof is lower than the threshold value Nr.