Selective Resistive Motor Braking for Compact Power Tool Heat Dissipation
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Solution Overview
Problem
Existing power tools with large, high-cost braking resistors for motor braking face issues of excess heat concentration and increased manufacturing costs, as well as limited space for heat dissipation.
Innovation Solution
A motor braking circuit with multiple resistive loads and field effect transistors (FETs) controlled by a motor controller, which selectively couples resistive loads to motor terminals, allowing for pulse width modulated control and regenerative braking to manage heat 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 brought to a complete stop within the prescribed time period, but excess heat is concentrated at one location and manufacturing costs increase
Solution Approach 1:
The single large braking resistor is divided into multiple smaller resistive loads (first resistive load, second resistive load, third resistive load) connected to different motor terminals. This segmentation distributes the heat generation across multiple locations, preventing excessive heat concentration at a single point while maintaining the required braking performance.
Solution Approach 2:
Multiple resistive loads are combined to work together as a braking system. The motor controller simultaneously activates multiple resistors during braking operations, combining their energy dissipation capabilities to achieve the required stopping performance while distributing thermal load across multiple components.
2Reliability
If a large braking resistor is used to absorb excess current during motor braking, then the motor can be brought to a complete stop within the prescribed time period, but manufacturing costs increase due to the resistor and heat dissipation components
Solution Approach 1:
The braking function is segmented across multiple smaller resistive loads rather than using one large resistor. This allows the use of smaller, less expensive components that are easier to manufacture and integrate into the power tool, reducing overall manufacturing costs while achieving the same braking performance.
Solution Approach 2:
The invention uses multiple smaller, less expensive resistive loads instead of a single large, costly braking resistor. These smaller resistors are cheaper to manufacture and require less expensive heat dissipation infrastructure, reducing the overall cost of the power tool while maintaining required braking performance.
3Reliability
If a large braking resistor is used to absorb excess current during motor braking, then the motor can be brought to a complete stop within the prescribed time period, but additional space is required for heat dissipation components
Solution Approach 1:
The braking function is distributed across multiple smaller resistive loads positioned at different locations within the motor assembly. This segmentation eliminates the need for a large centralized heat dissipation structure, as each small resistor generates less heat and can be managed with minimal local cooling, thereby saving space in the power tool design.
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
This solution reduces manufacturing costs, improves heat management by distributing heat over a larger area, and provides additional space-saving options while effectively braking the motor within prescribed time limits.
Implementation Method 1
one or more resistive loads of the braking circuit may include three resistive loads, one for each of the three motor terminals
Implementation Method 2
The one or more braking switches may include field effect transistors (FETs) controlled by the motor controller. The motor controller may perform a pulse width modulated (PWM) control of the one or more braking switches to brake the motor
Data Source
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.