AC Power Tool Control Circuit for Reliable Switch Activation
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Solution Overview
Problem
Existing hand-held power tools with electric motors face issues of 'misfires' where the circuit breaker fails to remain conductive during AC voltage half-waves, leading to inefficient motor operation and increased hardware and complexity costs for monitoring and re-ignition.
Innovation Solution
The electronic control device incorporates a bias output and detection input connected via a voltage divider, allowing immediate monitoring of the circuit breaker's state after triggering and repeated re-ignition within a half-cycle if necessary, with a limited number of checks and firings to ensure reliable activation and minimize hardware complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage measurement at the circuit breaker is used for ignition monitoring, then reliable detection of circuit breaker state is achieved, but hardware complexity and cost increase
Solution Approach 1:
A voltage divider circuit with two resistors is introduced as an intermediary between the circuit breaker and the control device. This simple passive circuit divides the voltage signal and provides a scaled-down version to the detection input, enabling reliable voltage measurement without requiring complex high-voltage measurement circuitry or amplifiers.
Solution Approach 2:
The patent replaces complex electronic measurement systems (such as low-impedance measuring resistors with amplifiers) with a simple passive voltage divider circuit. This substitution maintains detection reliability while dramatically reducing hardware complexity and cost.
2Reliability
If multiple ignition pulses are output at specified time intervals, then circuit breaker conduction is ensured, but unnecessary ignition current is consumed and power supply complexity increases
Solution Approach 1:
The control device continuously monitors the voltage at the detection input and uses this feedback information to determine whether the circuit breaker is properly conductive. Based on this feedback, the control device intelligently decides whether to output additional ignition pulses, avoiding unnecessary current consumption while ensuring reliable motor operation.
Solution Approach 2:
Instead of continuously outputting ignition pulses at fixed intervals, the system applies ignition pulses only when necessary - specifically when the detection input indicates the circuit breaker is not conductive. This partial action approach ensures reliability while minimizing energy waste from excessive ignition current.
3Measurement precision
If ignition monitoring is implemented with low-impedance measuring resistor and amplifier, then accurate motor current measurement is achieved, but hardware complexity and cost increase
Solution Approach 1:
The voltage divider circuit acts as an intermediary that provides adequate voltage signal levels directly to the detection input without requiring amplification. This eliminates the need for complex amplifier arrangements while maintaining sufficient measurement precision for detecting circuit breaker state and controlling ignition timing.
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
This solution ensures reliable and economical activation of the electric motor by reducing misfires and minimizing unnecessary ignition pulses, achieving efficient motor operation with low hardware and programming requirements.
Implementation Method 1
a voltage divider having a summation point, and the control device is also designed in this way that the potential at the detection input is monitored
Data Source
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AI summary
The invention relates to an electrical power tool, particularly an electric hand power tool, for operating with alternating current, having an electric motor (2), and electronic control device (6), and an electrical power switch (4) for actuating the electric motor (2), wherein the electronic control device (6) comprises a bias voltage output (16) and a detection input (18), connected to each other by means of a voltage divider (26) comprising a summation point (20) and to the side of the power switch (4) facing the electric motor (2), and the control device (6) is further designed such that the potential at the detection input (18) is monitored after actuating the power switch (4) and used for checking whether the power switch (4) is conducting, and that it is actuated again if the power switch (4) was not conducting or returned to the non-conducting state during the monitoring, and that said checking and any renewed actuation of the power switch (4) is repeated within a half-wave of the alternating voltage.