Power Tool Start-Up Constant-Clutch Control for Anti-Kickback

Solution Overview

Problem

Existing anti-kickback mechanisms in power tools, such as large angle grinders, often inadvertently shut down during start-up due to high current spikes or slow speed ramps, leading to frustrating and unnecessary shutdowns.

Innovation Solution

Implementing a constant-clutch mode at start-up, where the anti-kickback protection thresholds are temporarily modified to allow the motor speed to ramp up without shutting down the tool, and extending the protection time limits for a set period to prevent premature shutdowns.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If anti-kickback protection mechanisms are implemented with standard protection time limits, then kickback conditions during normal operation can be detected and protected against, but the motor shuts down prematurely during start-up due to high current spikes and slow speed ramps

Engineering Contradiction:

Improveanti-kickback protectionVSAvoidstart-up operation continuity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The protection time limit is made dynamic rather than static. The controller automatically adjusts the protection time limit based on the motor's operational state: a first (extended) protection time limit is applied during start-up period, and a second (standard) protection time limit is applied during normal operation. This dynamic adjustment allows the system to tolerate high current spikes during start-up while maintaining sensitive kickback detection during normal operation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The key parameter being changed is the protection time limit duration. The system transitions between two distinct time limit values based on operational phase. During start-up, the extended time limit prevents premature shutdown despite temporary overcurrent conditions. Once the motor reaches normal operating speed, the system switches to the standard time limit for normal kickback protection.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the protection time limit is extended to allow motor speed to ramp up during start-up, then unnecessary shutdowns are prevented, but the system may fail to detect actual kickback conditions during normal operation

Engineering Contradiction:

Improvestart-up operation continuityVSAvoidkickback detection accuracy

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The protection time limit is made dynamic rather than static. The controller automatically adjusts the protection time limit based on the motor's operational state: a first (extended) protection time limit is applied during start-up period, and a second (standard) protection time limit is applied during normal operation. This dynamic adjustment allows the system to tolerate high current spikes during start-up while maintaining sensitive kickback detection during normal operation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system operates in periodic phases: a start-up period followed by normal operation period. During the start-up period, the extended protection time limit is active. Once the motor reaches normal operating speed, the system transitions to the normal operation period where the standard protection time limit applies. This periodic switching ensures appropriate protection characteristics for each operational phase.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS12266918B2Constant-clutch operation at power tool start-up

Publication Date: 2025.04.01 BLACK & DECKER CORP

AI summary

A method of operating a power tool having a motor and a controller is provided. The method includes: setting a protection time limit associated with a condition of the motor; taking protective action to shut down the motor if the condition of the motor persists for a duration of the protection time limit; and in response to occurrence of the condition during a start-up period of operation of the motor, extending the protection time limit for a duration of a constant-clutch time period to allow an output speed of the motor to reach or exceed a speed threshold, and taking protective action to shut down the motor if the output speed of the motor remains below the speed threshold for the duration of the constant-clutch time period.