Power Tool Anti-Kickback Control With False Trip Screening
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Solution Overview
Problem
Existing power tools with anti-kickback control systems often experience false trips or nuisance initiations, particularly when operating under no load or in hammer only mode, due to the inability to accurately distinguish between valid and invalid kickback conditions.
Innovation Solution
A power tool control system that utilizes a current sensor and a rotational motion sensor to differentiate between valid and invalid kickback conditions by monitoring motor current and rotational movement, and initiates protective operations such as interrupting power, reducing motor power, or actuating a clutch only when a valid kickback is detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If protective operations are initiated frequently, then operator safety is improved, but tool productivity decreases due to nuisance initiations
Solution Approach 1:
The system performs preliminary analysis of motor current characteristics before initiating protective operations. By evaluating current patterns, load conditions, and operational mode in advance, the system can predict whether a detected anomaly represents a genuine kickback event requiring intervention or a normal operational variation. This preliminary assessment prevents nuisance initiations that would disrupt tool productivity while maintaining operator safety for genuine kickback events.
2Device complexity
If a single sensor system is used for kickback detection, then device complexity is reduced, but measurement precision decreases leading to false indications
Solution Approach 1:
The control system makes the motor current sensor multi-functional by using it for both motor control and kickback detection purposes. The same current measurements used for basic motor operation are also analyzed for kickback event detection, eliminating the need for additional dedicated sensors. This universal use of the current sensor maintains device simplicity while achieving sufficient measurement precision through sophisticated signal analysis algorithms that can distinguish genuine kickback events from normal operational variations.
Data Source
AI summary
A power tool includes a housing, a motor received in the housing, an output driven by the motor, and a control system. The control system includes a rotational motion sensor configured to generate a rotational motion signal that corresponds to a rotational motion of the housing about an axis, a current sensor configured to generate a motor current signal that corresponds to an amount of current drawn by the motor, and a control circuit that is configured to receive the rotational motion signal and the motor current signal and to control operation of the motor. The control circuit is configured: (a) to determine, based on the current signal, whether a detected kickback condition is likely to be false; (b) to determine, based upon the rotational motion signal, whether an uncontrolled kickback condition has occurred; and (c) to initiate one or more protective operations upon determining that an uncontrolled kickback condition has occurred and is not likely to be false.