Power Tool Current Limiting With PWM Duty Ratio Control

Solution Overview

Problem

Power tools, such as handheld pruners and chainsaws, face reduced runtime and potential battery damage due to excessive current draw during high load situations, leading to inefficient energy use and user inconvenience.

Innovation Solution

A power tool system with a current sensor, an inverter bridge, and an electronic processor that measures average current and adjusts the PWM duty ratio proportionally to a predetermined threshold, reducing power delivery to the motor and preventing excessive current draw.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the motor operates at high current draw during high load situations, then the cutting power and performance are improved, but the runtime is reduced and battery damage may occur

Engineering Contradiction:

Improvecutting powerVSAvoidruntime

Core Design Contradiction:

PowerVSDuration of action of moving object

Solution Approach 1:

The system dynamically adjusts the PWM duty ratio based on real-time current measurements. The electronic processor continuously monitors current draw and modifies the duty ratio to maintain optimal power delivery while preventing excessive current that would reduce runtime or damage the battery. This dynamic adaptation allows the motor to operate at high power when needed while automatically reducing power consumption when loads decrease.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The current sensor provides continuous feedback to the electronic processor about the actual current draw. The processor uses this feedback to determine when the average current exceeds the threshold and adjusts the PWM duty ratio proportionally to the deviation. This closed-loop feedback system ensures the motor operates within safe current limits while maximizing runtime.

Inventive Principle:

Principle #23Feedback

2Power

If the motor operates at high current draw during high load situations, then the cutting performance is improved, but heat generation increases

Engineering Contradiction:

Improvecutting powerVSAvoidheat generation

Core Design Contradiction:

PowerVSTemperature

Solution Approach 1:

The system dynamically adjusts the PWM duty ratio based on real-time current measurements. The electronic processor continuously monitors current draw and modifies the duty ratio to maintain optimal power delivery while preventing excessive current that would generate harmful heat. This dynamic adaptation allows the motor to operate at high power when needed while automatically reducing power consumption when loads decrease.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The current sensor provides continuous feedback to the electronic processor about the actual current draw. The processor uses this feedback to determine when the average current exceeds the threshold and adjusts the PWM duty ratio proportionally to the deviation. This closed-loop feedback system ensures the motor operates within safe current limits while maximizing runtime.

Inventive Principle:

Principle #23Feedback

3Power

If a fixed high PWM duty ratio is used, then the motor provides consistent high power, but the current draw becomes excessive during varying load conditions

Engineering Contradiction:

Improvemotor powerVSAvoidcurrent consumption

Core Design Contradiction:

PowerVSUse of energy by moving object

Solution Approach 1:

The system dynamically adjusts the PWM duty ratio based on real-time current measurements. The electronic processor continuously monitors current draw and modifies the duty ratio to maintain optimal power delivery while preventing excessive current that would reduce runtime or damage the battery. This dynamic adaptation allows the motor to operate at high power when needed while automatically reducing power consumption when loads decrease.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the PWM duty ratio parameter dynamically based on measured current conditions. When the average current exceeds the predetermined threshold, the processor reduces the duty ratio proportionally to the deviation. This parameter adjustment optimizes energy usage by matching power delivery to actual load requirements rather than maintaining a fixed high duty ratio.

Inventive Principle:

Principle #35Parameter changes

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 extends the runtime of power tools by managing current consumption, reducing heat generation, and enhancing user experience by minimizing frequent stoppages and start-ups.

Implementation Method 1

a current sensor configured to measure a current flow to the motor

Methodology Applied

Scientific EffectElectrical measurement: Ohmmeter

Implementation Method 2

an inverter bridge selectively providing power from a battery pack to the motor, and an electronic processor coupled to the current sensor and the inverter bridge. The PWM duty ratio corresponds to a PWM signal provided to the inverter bridge

Methodology Applied

Scientific EffectPulse width modulation: Phase Modulation

Data Source

PatentUS11811347B2Selectable current limiting for power tool

Publication Date: 2023.11.07 MILWAUKEE ELECTRIC TOOL CORP

AI summary

Selectable current limiting for a power tool. One embodiment provides a method for selectable current limiting for a power tool including determining, using a current sensor, an average current and determining whether the average current exceeds a predetermined current threshold. The method also includes determining a deviation of the average current from the predetermined current threshold and reducing a PWM duty ratio proportional to the deviation of the average current from the predetermined current threshold. The PWM duty ratio corresponds to a PWM signal provided to an inverter bridge.