Power Tool Trigger Switch Vibration Detection
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Solution Overview
Problem
Power tools with motor control systems that rely solely on the ON/OFF state of a trigger switch are prone to unintended motor stoppage due to vibrations or noise, leading to incorrect detection of the operator's hand position, resulting in premature motor shutdown.
Innovation Solution
A power tool system that utilizes a speed contact potentiometer to maintain motor rotation if the speed signal level is above a set threshold, even when the main contact is turned OFF, and stops the motor only if the speed signal is below the threshold or if the main contact remains OFF for a predetermined period, ensuring accurate detection of the operator's hand position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the motor start/stop is controlled by only the ON/OFF state of the main contact, then the control system is simple, but the motor may stop unintentionally due to vibration, noise, or other reasons even when the operator has not removed hands from the trigger switch
Solution Approach 1:
The trigger switch is segmented into two independent contacts: the main contact (ON/OFF switch) and the speed contact (potentiometer). The main contact provides basic start/stop control, while the speed contact provides continuous speed signal output. This segmentation allows the system to use both contacts together for more reliable operation detection, preventing unintentional motor stoppage while maintaining relatively simple control logic.
Solution Approach 2:
The speed contact acts as an intermediary element that provides additional information about the operator's intent. By monitoring both the main contact state and the speed contact output level, the control system can distinguish between intentional stop commands and unintentional interruptions caused by vibration or noise, thereby improving reliability without significantly increasing complexity.
2Speed
If the main contact is used alone for control, then the response is immediate, but false stoppage occurs due to vibration or noise affecting the contact state
Solution Approach 1:
The speed contact provides continuous feedback about the trigger switch position through its output voltage level. The control system monitors this feedback signal alongside the main contact state to accurately determine whether the operator intends to stop the motor. This feedback mechanism prevents false stoppage detection caused by vibration or noise while maintaining immediate response when the operator genuinely releases the trigger.
Solution Approach 2:
The system performs preliminary verification by checking both the main contact state and the speed contact output level before executing a stop command. This preliminary action ensures that the motor stops only when both indicators confirm the operator's intent, preventing premature shutdown due to transient disturbances while maintaining rapid response when conditions clearly indicate intentional stopping.
Data Source
AI summary
The controller (9) determines the presence or absence of operation of the trigger switch (8) according to an ON/OFF state of the main contact (8b) of the trigger switch (8) and designating the rotation speed of the motor (3) based on a signal outputted from the speed contact (8a). The controller (9) stops the rotation of the motor (3), after the trigger switch (8) is activated and the main contact (8b) is turned ON and the motor (3) is driven according to a signal outputted from the speed contact (8a), when an OFF state of the main contact (8b) is detected, only in the case where a signal value outputted from the speed contact (8a) is a predetermined value or less.