Handheld Power Tool Drive Circuit for Fast Motor Braking
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Solution Overview
Problem
Existing electric handheld power tools face challenges in safely stopping the drill from rotating when wedged, leading to potential injury risks and increased carbon brush wear due to high braking currents and unregulated motor polarity reversals using TRIACs.
Innovation Solution
An electric drive unit with a semiconductor-based actuating circuit that independently controls rotor and stator currents, allowing precise braking with reduced carbon brush wear and increased safety by limiting rotor current and regulating stator current, using a minimal number of semiconductor components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If high braking currents are used to stop the motor quickly for safety, then the braking time is reduced, but carbon brush wear increases significantly
Solution Approach 1:
The patent changes the control parameters by independently regulating rotor and stator currents through a semiconductor-based actuating circuit. By controlling the rotor current separately from the stator current, the system can apply sufficient braking torque while limiting the current that causes brush wear, achieving quick stopping without excessive brush consumption
Solution Approach 2:
The patent replaces the mechanical slip clutch with an electronic braking system using semiconductor components (IGBTs, MOSFETs, or bipolar transistors). This electronic control system can precisely regulate braking currents without the mechanical wear inherent in traditional slip clutches, eliminating the trade-off between braking speed and brush wear
2Adaptability or versatility
If TRIACs are used for polarity reversal in the bridge circuit, then the circuit can be operated with AC voltage, but the polarity reversal can only occur during zero crossing causing time delay up to 10 ms
Solution Approach 1:
The patent substitutes TRIACs with semiconductor switching components (IGBTs, MOSFETs, or bipolar transistors) that can change state instantaneously without requiring zero-crossing conditions. This replacement enables immediate polarity reversal when braking is initiated, eliminating the up to 10 ms delay inherent in TRIAC-based systems while maintaining AC voltage operation capability
Solution Approach 2:
The actuating circuit is designed to pre-position the semiconductor switches in optimal states before braking is needed. The circuit can immediately respond to braking commands by having the switches ready to change polarity without waiting for AC voltage zero crossings, thus eliminating response delays
3Force
If high braking currents are applied to achieve quick stopping, then the braking torque is sufficient, but brush sparking and heating of the electric motor increase
Solution Approach 1:
The patent independently controls rotor and stator current parameters through the semiconductor actuating circuit. By optimizing the rotor current magnitude and waveform separately from the stator current, the system generates sufficient braking torque while limiting excessive current that causes brush sparking and motor heating, thus resolving the contradiction between braking force and thermal effects
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 solution enables safe and efficient braking of the electric motor within milliseconds, reducing carbon brush wear and extending maintenance intervals while maintaining high braking torque, thus enhancing the service life and safety of the electric handheld power tool.
Implementation Method 1
The stator winding (12) is connected via a first node (10) to a stator-side first half-bridge (40) comprising a first semiconductor component (201) and a second semiconductor component (202)... The rotor winding (14) is connected to a third node (18)... The actuating circuit (4) comprises a third semiconductor component (203)... In this way, the rotor current and the stator current of the electric motor can be set precisely and independently of one another
Implementation Method 2
an electric motor (7) having a stator winding (12) and a rotor winding (14)... an energy source (2) for driving the electric motor (7)... When the respective semiconductor component is moved to a conductive state, a current can flow through the semiconductor component
Data Source
AI summary
An electric drive unit for an electric handheld power tool, having an electric motor with a stator winding and a rotor winding, an actuating circuit for actuating the electric motor and a connection unit for coupling an energy source for driving the electric motor, wherein the stator winding is connected via a first node to a stator-side first half-bridge including a first semiconductor component and a second semiconductor component and is connected via a second node to the rotor winding, wherein the rotor winding is connected to a third node which is connected via a conductive component to the connection unit, and wherein the actuating circuit includes a third semiconductor component which is connected via the second node to the rotor winding and the stator winding and which is connected via a fourth node directly to the connection unit.