Capacitive Trigger Switch Sensing for Magnetic Field Immunity
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Solution Overview
Problem
Trigger switches in power tools that use magnetic sensors can operate erratically due to external magnetic fields, leading to inaccurate detection of trigger depression amounts.
Innovation Solution
A trigger switch design incorporating a movable and fixed electrode forming a capacitor, where the capacitance changes with trigger depression, allowing contactless detection of trigger movement unaffected by external magnetic fields, using a capacitive sensing mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a magnetic sensor is used to detect trigger depression amount contactlessly, then the service life is extended, but the detection accuracy deteriorates under external magnetic fields
Solution Approach 1:
The patent replaces the magnetic sensor-based detection system with a capacitive sensor system. The capacitive sensor detects trigger depression amount through changes in capacitance between a fixed electrode and a movable electrode, eliminating dependence on magnetic fields while maintaining contactless detection and extended service life.
Solution Approach 2:
The patent changes the detection parameter from magnetic field interaction to capacitance variation. By measuring the change in capacitance value as the movable electrode approaches the fixed electrode during trigger depression, the system achieves accurate detection without being affected by external magnetic fields.
2Reliability
If a magnetic sensor is used for contactless detection, then friction is reduced, but reliability deteriorates in environments with strong magnetic fields
Solution Approach 1:
The patent substitutes the magnetic sensing mechanism with a capacitive sensing mechanism. The capacitive sensor uses electrical field interaction between electrodes rather than magnetic field interaction, making the system reliable in environments with strong magnetic fields while maintaining contactless operation and low friction.
3Measurement precision
If the electrode area is increased to improve detection sensitivity, then the detection precision is improved, but the device complexity increases
Solution Approach 1:
The patent enhances detection precision not by increasing the two-dimensional area of the electrodes, but by exploiting the third dimension - the distance between the fixed electrode and movable electrode. As the trigger is depressed, the movable electrode approaches the fixed electrode, causing significant capacitance change that provides high detection sensitivity without requiring large electrode areas or complex structures.
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 capacitive sensing mechanism provides reliable and long-lasting detection of trigger depression amounts, reducing friction and maintaining accuracy even in environments with strong magnetic fields.
Implementation Method 1
The fixed electrode forms a capacitor together with the movable electrode. The capacitor formed by the movable electrode and the fixed electrode has a capacitance changing as the movable electrode moves.
Data Source
AI summary
A trigger switch according to one or more embodiments may include a first conductive plate (movable electrode) movable in response to movement of a trigger receiving a depressing operation, and a second fixed electrode (fixed electrode) located adjacent to a movable range of the first conductive plate with a space in between. The second fixed electrode forms a capacitor together with the first conductive plate. The capacitor formed by the first conductive plate and the second fixed electrode has a capacitance that changes as the first conductive plate moves.