Selective Braking Resistor Layout for Fast Motor Stops
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Solution Overview
Problem
Existing power tools use large, high-cost braking resistors that generate excess heat and occupy space, increasing manufacturing costs and heat management challenges.
Innovation Solution
A motor braking circuit with selectively connectable resistive loads, controlled by a motor controller, which determines the need for braking based on system impedance or current thresholds, using multiple smaller resistors to dissipate heat over a larger area and reduce component size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large braking resistor is used to absorb excess current during motor braking, then the motor can be stopped within the required time period, but the resistor generates excess heat concentrated at one location and increases manufacturing cost
Solution Approach 1:
The patent divides the single large braking resistor into multiple smaller resistors (first braking resistor and second braking resistor). Each resistor handles a portion of the braking current, distributing the heat generation across multiple components rather than concentrating it in one location. This segmentation maintains the required braking performance while improving heat management.
2Reliability
If a large braking resistor is used to absorb excess current during motor braking, then the motor can be stopped within the required time period, but the resistor and heat dissipation components increase manufacturing cost
Solution Approach 1:
The patent segments the braking function across multiple smaller resistors rather than using one large resistor. This approach reduces manufacturing costs because smaller resistors are less expensive to produce and purchase, while still achieving the required braking performance through their combined effect.
Solution Approach 2:
The patent uses multiple smaller, less expensive resistors instead of one large, costly resistor. The smaller resistors can be more easily replaced if needed and represent a lower initial investment, making the overall system more cost-effective while maintaining the necessary braking capability.
3Reliability
If a large braking resistor is used to absorb excess current during motor braking, then the motor can be stopped within the required time period, but the resistor occupies space and reduces layout flexibility
Solution Approach 1:
The patent divides the braking function into multiple smaller resistors that occupy less total space than a single large resistor would require. The segmented arrangement allows for more flexible PCB layout and better utilization of available space within the power tool housing.
Solution Approach 2:
The patent arranges the multiple braking resistors in a distributed configuration across different areas of the circuit board rather than concentrating them in one location. This spatial distribution optimizes the use of available space and improves thermal management by spreading heat generation across different zones.
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
Reduces manufacturing costs and improves heat management by using smaller resistors spread across multiple paths, achieving faster motor stops without high heat density and providing space-saving layout options.
Implementation Method 1
A motor braking circuit for a power tool motor includes one or more resistive loads and a braking circuit selectively coupling the one or more resistive loads to motor terminals of the motor
Data Source
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Figure 3A
AI summary
Apparatus and method for motor braking using selectively connectable resistance. The method includes controlling, using a motor controller of the power tool, a power switching network to drive a motor of the power tool in response to actuation of a user input and determining, using the motor controller, a variable tool characteristic. The method further includes determining, using the motor controller, that the user input is de-actuated. The method also includes controlling, using the motor controller, the power switching network to brake the motor when the variable tool characteristic satisfies the tool characteristic threshold and controlling, using the motor controller, a braking circuit to brake the motor when the variable tool characteristic does not satisfy the tool characteristic threshold. The braking circuit includes one or more resistive loads and is selectively coupled to the motor terminals of the motor.