Electric Tool Protection Circuit for Accidental Startup Blocking
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Solution Overview
Problem
Electric tools such as impact wrenches and angle grinders pose safety hazards due to the risk of accidental startup when the power is turned on and a battery pack is connected, leading to potential injuries from high rotational speeds.
Innovation Solution
Incorporating a protection circuit between the master switch and the control circuit that disconnects the power supply when the master switch is in the on state before the tool interface connects to the power supply, ensuring safe operation by preventing unintended motor activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a locking piece is provided on an operation member to maintain an on state of the switch, then ease of operation is improved, but safety deteriorates due to risk of accidental startup
Solution Approach 1:
The protection circuit performs preliminary detection of the master switch state before power connection. When the master switch is already in the on state before the battery pack is connected, the protection circuit preemptively prevents power transmission to the control circuit, thereby avoiding accidental startup. This preliminary action resolves the contradiction by maintaining the convenient locked-on functionality while adding a safety check that prevents harmful accidental activation.
2Productivity
If the master switch is in the on state before power connection, then operational readiness is improved, but safety deteriorates due to potential accidental startup
Solution Approach 1:
The protection circuit acts as an intermediary between the master switch and the control circuit. It monitors the master switch state and the power connection status, and only allows power transmission when both conditions are safe (master switch off before connection, or master switch turned on after connection). This intermediary function resolves the contradiction by maintaining operational readiness while filtering out unsafe conditions that could cause accidental startup.
3Object-affected harmful factors
If a protection circuit is added to prevent accidental startup, then safety is improved, but device complexity increases
Solution Approach 1:
The protection circuit utilizes the existing master switch state and power connection status signals to automatically determine whether to block or allow power transmission. The circuit self-regulates based on the detected conditions without requiring additional control inputs or complex logic. This self-service approach resolves the contradiction by providing comprehensive safety functionality while keeping the circuit design relatively simple and integrated with existing components.
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 protection circuit effectively prevents the electric tool from starting when the operation switch is misoperated, enhancing safety by ensuring the tool only activates when intentionally started, thus reducing the risk of injury.
Implementation Method 1
the first power supply branch includes a capacitor electrically connected to the master switch, and the capacitor is not powered on in response to the master switch being in the on state before the tool interface connects to the power supply
Implementation Method 2
the first triode is configured to turn on in response to the capacitor discharging
Data Source
AI summary
An electric tool includes a housing, a motor, a tool interface, a control circuit, a master switch, and a protection circuit. The tool interface is configured to connect to a power supply to supply power to the motor. The master switch is disposed on a current path formed by the tool interface and the control circuit. The master switch has an on state in which electric connection between the tool interface and the control circuit is on and an off state in which the electric connection between the tool interface and the control circuit is off. The protection circuit is connected between the master switch and the control circuit and is configured to disconnect connection between the tool interface and the control circuit in response to the master switch being in the on state before the tool interface connects to the power supply.