Power Tool Under-Voltage Control With Dual Shutdown Thresholds
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Solution Overview
Problem
Power tools with existing under-voltage protection features shut down abruptly when sudden voltage drops occur, failing to recover and complete operations effectively.
Innovation Solution
Implementing multiple voltage thresholds for under-voltage protection, where a first threshold reduces the motor current by adjusting the PWM signal duty cycle to allow voltage recovery, and a second threshold initiates shutdown, using a motor, power source, voltage sensor, and controller to selectively provide power and monitor voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single voltage threshold is used for under-voltage protection, then the power tool can be protected from damage, but the tool shuts down abruptly without opportunity for recovery
Solution Approach 1:
The single voltage threshold is segmented into two distinct thresholds: a first threshold that triggers duty cycle reduction and a second threshold that triggers shutdown. This segmentation allows the system to respond progressively to voltage drops, first attempting recovery and then shutting down only if necessary, thereby maintaining both protection and productivity.
Solution Approach 2:
The system dynamically adjusts the PWM duty cycle in response to voltage conditions. When voltage drops to the first threshold, the duty cycle is reduced to lower motor current and allow voltage recovery. This dynamic adjustment enables the tool to adapt to changing voltage conditions rather than using a static on/off approach.
2Productivity
If the power tool reduces duty cycle to allow voltage recovery, then operation can be maintained, but the voltage must remain above a critical level
Solution Approach 1:
The system continuously monitors voltage levels and provides feedback to the controller. When voltage drops to the first threshold, the controller reduces duty cycle and continues monitoring. If voltage recovers above the first threshold, normal operation resumes. If voltage continues to drop to the second threshold, shutdown occurs. This feedback loop ensures operation is maintained whenever possible while protecting against critical voltage levels.
3Productivity
If multiple voltage thresholds are implemented, then operation recovery is enabled, but the control system complexity increases
Solution Approach 1:
The system changes the parameter being controlled (PWM duty cycle) in response to changes in another parameter (voltage level). By monitoring voltage and adjusting duty cycle accordingly, the system enables recovery without adding complex hardware. The controller simply modifies an existing control parameter based on voltage threshold comparisons.
Data Source
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.