Saw Motor Braking Circuit With Feedback Current Limiting
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Solution Overview
Problem
Existing power tools face safety hazards and battery damage due to excessive braking forces and feedback currents during the braking process, particularly in large-inertia sawing products like miter saws and table saws.
Innovation Solution
A sawing tool with a control circuit that adjusts the duty cycle of a control signal to manage the feedback current, using a driver circuit with high-side and low-side switching elements, and a controller to switch between brake and freewheeling modes, ensuring the feedback current does not exceed a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If short-circuit braking is used to brake the motor, then braking force is generated, but too large braking force is generated causing safety hazards and potential damage
Solution Approach 1:
The patent applies dynamics by switching the braking method from static short-circuit braking to dynamic regenerative braking. The motor transitions from generating large braking force through resistance to generating controlled braking force by feeding energy back to the power supply, making the braking force adjustable and safer.
Solution Approach 2:
The patent converts the harmful reverse energy backflow during braking into a beneficial resource by implementing regenerative braking. The energy that would normally be wasted or cause damage is instead fed back to the power supply through the feedback circuit, reducing energy loss and eliminating safety hazards.
2Force
If soft braking with feedback current is used to reduce braking force, then braking force is reduced, but relatively large feedback current damages the battery pack
Solution Approach 1:
The patent implements feedback control by detecting the feedback current during regenerative braking and comparing it with a preset threshold. When the feedback current exceeds the threshold, the control circuit adjusts the duty cycle of PWM signals to limit the current, preventing battery pack damage while maintaining effective braking.
Solution Approach 2:
The patent changes the parameter of duty cycle dynamically during braking. By adjusting the duty cycle of PWM signals based on feedback current magnitude, the system optimizes the balance between braking effectiveness and battery pack protection, ensuring feedback current remains within safe limits.
3Measurement precision
If feedback current is increased to achieve better braking control, then braking precision is improved, but battery pack is damaged
Solution Approach 1:
The patent uses feedback current detection to achieve precise braking control while protecting the battery pack. The control circuit continuously monitors feedback current and adjusts the duty cycle accordingly, maintaining optimal braking performance without exceeding safe current thresholds that would damage the battery.
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
Prevents battery damage and ensures safe braking by maintaining the feedback current within a safe limit, thereby extending the battery life and ensuring reliable motor braking.
Implementation Method 1
the motor to generate a feedback current during the braking process
Data Source
AI summary
A sawing tool includes a motor; a battery pack supplying power to the motor; and a control circuit for controlling the motor to rotate or brake. The control circuit includes a driver circuit including multiple high-side switching elements and multiple low-side switching elements; and a controller electrically connected to at least the driver circuit and outputting a control signal to control the states of the multiple high-side switching elements and the multiple low-side switching elements. The controller is configured to: in response to a brake signal, control the driver circuit to operate in an energy feedback state and adjust the duty cycle of the control signal to adjust the magnitude of the feedback current in the energy feedback state. The energy feedback state includes a brake mode and a freewheeling mode; and the feedback current generated in the freewheeling mode is fed back to the battery pack.