Brushless Circular Saw Field Weakening for Compact Peak Power
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Solution Overview
Problem
Existing circular saws face challenges in optimizing power-to-volume and power-to-weight ratios while maintaining compact size and efficiency, especially when using battery power sources.
Innovation Solution
A circular saw design featuring a 5⅜-inch diameter saw blade, a brushless DC motor, and an electronic controller that adjusts conduction angle and duty cycle through PWM signals, along with field weakening operations, to enhance power output while fitting within a compact rectangular prism and achieving specific power-to-volume and power-to-weight ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a compact circular saw design is used, then the volume is reduced, but the power output is limited
Solution Approach 1:
The patent applies parameter changes by implementing field weakening control that dynamically adjusts the motor's magnetic field strength and conduction angle. This allows the motor to operate at higher speeds and deliver peak power output that exceeds the typical power-density limits of compact motors, achieving 500-600 Watts from a sub-450 cubic inch housing.
2Weight of moving object
If a compact circular saw design is used, then the weight is reduced, but the power output is limited
Solution Approach 1:
The field weakening control system enables the motor to operate beyond its base speed rating by reducing the magnetic field strength. This parameter change allows the motor to deliver high peak power (500-600 Watts) from a lightweight sub-10-pound saw, achieving power-to-weight ratios of 105-150 Watts/lb.
3Power
If field weakening operation is applied, then the peak power is increased, but the efficiency is reduced
Solution Approach 1:
The control system uses periodic PWM (pulse-width modulation) to deliver power to the motor. By switching the power delivery in controlled pulses rather than continuous operation, the system can achieve peak power output during field weakening while managing average power consumption and heat generation, thereby mitigating efficiency losses.
Solution Approach 2:
The system implements feedback control by monitoring motor current, speed, and temperature. This feedback allows the controller to adjust the field weakening magnitude and PWM duty cycle in real-time, optimizing the balance between peak power delivery and energy efficiency, and preventing excessive energy loss during high-power 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
The design achieves peak power-to-volume ratios of 1.00 to 2.00 Watts/in.³ and power-to-weight ratios of 105 to 150 Watts/lb., ensuring high power efficiency and compactness for portable use.
Implementation Method 1
a brushless direct current (DC) motor positioned within the housing assembly and operable to rotate the output shaft
Implementation Method 2
supply a pulse-width modulated ('PWM') signal having a duty cycle to the brushless DC motor to control a current of the brushless DC motor
Implementation Method 3
perform a field weakening operation to modify the conduction angle of the brushless DC motor
Data Source
AI summary
A circular saw may include a shoe and a blade guard assembly coupled to the shoe, the blade guard assembly including an upper blade guard and a lower blade guard movable between an extended position and a retracted position. A circular saw may include a housing assembly coupled to the blade guard assembly, an output shaft, and a blade clamp coupled to output shaft, the blade clamp configured to hold the saw blade. A circular saw may include a brushless direct current (DC) motor positioned within the housing assembly and operable to rotate the output shaft. A circular saw may include an electronic controller configured to perform a field weakening operation on the brushless DC motor.