Power Tool Under-Voltage Control With Staged PWM Current Limiting
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Solution Overview
Problem
Power tools with existing under-voltage protection features often shut down abruptly without opportunity to recover when sudden voltage drops occur, lacking adaptive mechanisms to manage voltage fluctuations effectively.
Innovation Solution
Implementing multiple voltage thresholds for under-voltage protection, where a controller reduces the duty cycle of a PWM signal to motor current when the voltage reaches a first threshold, allowing recovery, and shuts down when it drops below a second threshold, ensuring reliable operation and preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single voltage threshold is used for under-voltage protection, then the power tool shuts down quickly to protect the system, but it loses the opportunity to recover from temporary voltage drops
Solution Approach 1:
The single voltage threshold is segmented into multiple thresholds: a first threshold (e.g., 18V) that triggers duty cycle reduction, and a second threshold (e.g., 16V) that triggers shutdown. This segmentation allows the system to respond differently to varying severity levels of voltage drops, enabling recovery from minor fluctuations while protecting against severe conditions.
Solution Approach 2:
The protective response is made dynamic through the use of multiple thresholds and staged actions. Instead of a static single-threshold shutdown, the system dynamically adjusts its response based on the voltage level: mild drops trigger duty cycle reduction while severe drops trigger shutdown. This dynamic approach optimizes both protection and operational continuity.
2Productivity
If the power tool maintains full current during voltage drops, then it can complete its operation quickly, but it risks damaging the motor and power source
Solution Approach 1:
The system continuously monitors voltage levels and provides feedback to the controller, which adjusts the duty cycle accordingly. When voltage drops below the first threshold, the controller reduces the duty cycle to limit current draw, preventing motor damage while allowing the tool to continue operating at reduced capacity until voltage recovers or the second threshold is reached.
Solution Approach 2:
The system changes the operating parameter (duty cycle) in response to voltage conditions. By reducing the duty cycle when voltage drops occur, the system modifies the electrical parameters to prevent harmful effects while maintaining operational capability. This parameter adjustment allows the tool to adapt to changing voltage conditions and protect the motor.
3Reliability
If the power tool shuts down at the first voltage threshold, then it prevents damage effectively, but it cannot recover from temporary voltage fluctuations
Solution Approach 1:
The protective shutdown function is segmented into two stages: a first stage that reduces duty cycle to prevent damage during mild voltage drops, and a second stage that shuts down only when severe drops occur. This segmentation allows the system to withstand temporary fluctuations without unnecessary shutdowns, reducing operational interruptions while maintaining damage prevention.
Solution Approach 2:
The system provides a cushioning effect by reducing the duty cycle before a complete shutdown is necessary. This intermediate protective measure cushions the system against the full impact of voltage drops, allowing recovery without complete shutdown and thereby preventing unnecessary operational interruptions while still protecting against damage.
Data Source
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AI summary
Systems and methods for under-voltage protection features in power tools. One power tool provides a motor, a power source, a voltage sensor, and a controller. The power source is configured to selectively provide power to the motor. The voltage sensor is configured to sense a voltage of the power source. The controller is configured to monitor, with the voltage sensor, the voltage of the power source and reduce, when the voltage of the power source is less than or equal to a first threshold value, a current provided from the power source to the motor. The controller is configured to stop, when the voltage of the power source is less than or equal to a second threshold value, providing the current from the power source to the motor.