Power Tool Motor Control via PWM Duty Ratio Adjustment
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Solution Overview
Problem
Power tools with rechargeable battery packs often stop functioning prematurely due to over-discharging, caused by internal resistance and voltage drops, even when the battery state is still sufficient, leading to inefficient operation.
Innovation Solution
A power tool design that includes a voltage measurement unit and a control unit which adjusts the motor output by reducing the duty ratio of the PWM signal when the battery voltage approaches a predetermined threshold, thereby minimizing voltage drop and extending battery life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power tool stops the motor when battery voltage becomes lower than a predetermined value to prevent over-discharging, then the battery pack is protected from over-discharging, but the motor stops unnecessarily even when the actual state of charge is still sufficient
Solution Approach 1:
The control unit changes the PWM duty ratio parameter when battery voltage decreases, reducing it to a value smaller than before the voltage decrease. This adjusts the motor output to match the reduced battery voltage, preventing unnecessary motor stops while still protecting against over-discharging.
Solution Approach 2:
The system dynamically adjusts the PWM duty ratio based on real-time battery voltage measurements. When voltage decreases, the duty ratio is reduced accordingly, allowing the motor to continue operating at reduced power rather than stopping completely, thus maintaining operational continuity while protecting the battery.
2Ease of operation
If the duty ratio of PWM signal is reduced when battery voltage decreases, then the motor continues operating with reduced output, but the power output of the motor decreases
Solution Approach 1:
Instead of completely stopping the motor when battery voltage decreases, the system applies partial action by reducing the PWM duty ratio to a smaller value. This allows the motor to continue operating at reduced power output, maintaining sufficient functionality for less demanding tasks while extending battery life and avoiding unnecessary shutdowns.
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 allows the power tool to continue operating by reducing the load current and maintaining battery voltage, preventing unnecessary shutdowns and prolonging battery life by managing the motor output based on real-time voltage measurements.
Implementation Method 1
a voltage measurement unit that detects a battery voltage of the rechargeable battery
Implementation Method 2
the control unit drives the motor to generate an output that is smaller than that before the voltage decreased and became lower than or equal to the predetermined value
Data Source
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AI summary
A power tool includes a main body control unit (CP) that performs PWM control on an output of a motor (M). Whenever the voltage detected by a voltage measurement unit (41) decreases and becomes lower than or equal to a predetermined discharge detection voltage (S1), the main body control unit (CP) drives the motor (M) at a duty ratio that is lower than that before the voltage decreased and became lower than or equal to the predetermined value (S1).