Motor Voltage Choke Control for Hand-Held Power Tool Overload Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing control methods for power tools like circular saws are not suitable for hand-held tools, as they rely on controlled movement to prevent motor overloading, which is not applicable to hand-held devices, leading to potential motor damage due to excessive heat from increased resistance torque.
Innovation Solution
A control method that defines an overload condition when a predetermined threshold is exceeded beyond a limiting time period, reducing motor voltage to a choke value, allowing the user to reflexively pull back the tool, and automatically increasing it back to nominal after a choking period, without switching the motor off, thus minimizing work time loss and preventing further heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If motor voltage is reduced to protect the motor from overloading, then motor protection is improved, but productivity deteriorates due to work interruption
Solution Approach 1:
The control method dynamically adjusts motor voltage based on real-time current monitoring. When overload is detected, voltage is automatically reduced to protect the motor, then restored after the overload condition resolves, creating a dynamic protection mechanism that minimizes work interruption while ensuring motor safety
Solution Approach 2:
The system continuously monitors motor current and provides feedback to the voltage control mechanism. When current exceeds the threshold, the system responds by reducing voltage, and when current returns to normal levels, voltage is restored, creating a closed-loop feedback system that balances protection with productivity
2Temperature
If motor voltage is reduced to a choke value, then motor heating is prevented, but user perception of tool responsiveness deteriorates
Solution Approach 1:
The voltage reduction is applied periodically only when overload conditions are detected, rather than continuously. The system monitors current thresholds and applies voltage reduction intermittently, allowing the tool to maintain full responsiveness during normal operation while preventing overheating during overload conditions
3Reliability
If the control method uses stationary machine saw approach with controlled movement, then motor protection is achieved, but adaptability to hand-held power tools deteriorates
Solution Approach 1:
The control method is designed to be universally applicable to different power tool types including hand-held tools. It uses general motor parameters (current, voltage, power) rather than tool-specific movement control, making it adaptable to various tool configurations while maintaining effective motor protection
Solution Approach 2:
The system protects the motor by changing electrical parameters (voltage and current thresholds) rather than mechanical parameters (tool movement). This parameter-based approach allows the same control logic to work across different tool types without requiring tool-specific mechanical control mechanisms
Data Source
AI summary
A method for controlling a motor (2) which drives a disk-shaped tool (4) of a power tool (1) and to which a motor voltage in the amount of a nominal value is applied in an “on” position of a motor switch (6), includes determination of an actual motor current (IM) applied to the motor (2) and comparing it to a first predetermined threshold (GW1), and automatically triggering of a control process for protecting the motor (2) when an overload condition which is defined in that the first predetermined threshold (GW1) is exceeded beyond a first predetermined limiting time period (grDt1), is met, the control process including reduction of the motor voltage applied to the motor (2) by a magnitude that can be perceived by the user as a choke value.