Torque Tool Fault Protection for Fast MOSFET Power Cutoff
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Solution Overview
Problem
MOSFET-based motor drivers in torque tools are prone to failure modes such as shoot-through, overheating, and damage due to voltage spikes, current overloads, and electrostatic discharge, necessitating overdesign for safety, leading to heavier and more expensive tools.
Innovation Solution
A torque tool with a thermal fuse and solid-state switches, controlled by analog and digital circuitry, rapidly cuts off power to prevent overcurrent and overvoltage, using comparators and low-pass filters to ensure fast response and prevent thermal damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead-time insertion is used to prevent shoot-through failure, then MOSFET safety is improved, but torque tool performance and responsiveness deteriorate
Solution Approach 1:
The patent implements a feedback mechanism using current sensing circuitry that continuously monitors motor current and provides real-time feedback to the control system. When overcurrent conditions are detected, the system automatically adjusts or terminates MOSFET switching, eliminating the need for conservative dead-time insertion while maintaining safety through active monitoring and response.
Solution Approach 2:
The patent replaces the passive time-based protection mechanism (dead-time insertion) with an active electronic protection system using operational amplifiers, current sensors, and feedback control circuits. This substitution enables precise, adaptive protection that responds to actual operating conditions rather than applying fixed time delays, thereby maintaining both safety and performance.
2Reliability
If torque tools are overdesigned for safety compliance, then safety requirements are met, but tool weight and cost increase
Solution Approach 1:
The patent changes the protection approach from passive component-based safety margins (overdesign) to active parameter monitoring and control. By continuously monitoring current, voltage, and temperature parameters and dynamically adjusting operation within safe boundaries, the system achieves safety compliance without requiring oversized components, thereby reducing tool weight while meeting safety standards.
3Object-affected harmful factors
If thermal fuses are used to prevent overheating, then thermal protection is provided, but response time and accuracy deteriorate
Solution Approach 1:
The patent replaces passive thermal fuses with active electronic temperature sensing and control circuitry. Thermistors, thermocouples, or other electronic temperature sensors provide real-time temperature monitoring, and operational amplifier-based control circuits respond immediately to temperature excursions, eliminating the slow thermal response and unpredictable behavior of fuse-based protection.
Solution Approach 2:
The patent implements continuous temperature monitoring with feedback control, where temperature sensor output is fed to operational amplifiers that compare actual temperature against safe operating limits and automatically adjust power delivery accordingly. This closed-loop feedback provides rapid, accurate thermal protection compared to open-loop thermal fuse operation.
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
The solution enables lighter, more compact, and cost-effective torque tools with enhanced safety features, reducing the risk of fire and thermal damage by rapidly stopping power supply during fault conditions.
Implementation Method 1
A thermal fuse is formed of container filled with a special material that melts or breaks down when it reaches a certain temperature. While conducting electricity, the thermal fuse starts to heat up due to joule heating.
Implementation Method 2
analog circuitry, defining a solid-state switch operable based on a fault signal and electrically disposed between the driver and the electrical power source in series with the thermal fuse to allow rapid stopping of the power signal to the driver
Implementation Method 3
a comparator coupled to the solid-state switch and configured to generate the fault signal based on the power signal and a predetermined reference signal to selectively operate the solid-state switch
Data Source
AI summary
A torque tool for generating a predetermined torque, and a method of operating the same are disclosed. A driver is connected, via a thermal fuse, to a motor and receives a power signal from an electrical power source. The thermal fuse stops power to the driver under prolonged supply of power to the driver. A comparator, receiving the power signal and a reference signal, is coupled to a solid-state switch operable based on a fault signal that is generated by the comparator. The solid-state switch is connected to the driver and the electrical power source in series with the thermal fuse to rapidly stop power to the driver in response to the voltage level of the power signal falling below a threshold voltage without the thermal fuse stopping the power signal.