Electric Power Tool PWM Control for Stable Motor Acceleration
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Solution Overview
Problem
Variation in the magnitude of the power-supply voltage affects the acceleration of the motor in electric power tools, leading to undesirable variations in operations such as tightening torque.
Innovation Solution
An electric power tool with a drive circuit, voltage detector, and calculators to adjust the duty ratio of the pulse-width modulation signal based on the detected power-supply voltage, ensuring a controlled acceleration profile to reduce variations in motor speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the motor is driven directly with a fixed duty ratio, then the device complexity is reduced, but the motor acceleration varies due to power-supply voltage fluctuations
Solution Approach 1:
The control circuit detects the actual power-supply voltage magnitude and uses this feedback information to dynamically adjust the duty ratio of the PWM drive signal. This closed-loop feedback mechanism ensures that motor acceleration remains consistent regardless of voltage fluctuations, directly resolving the contradiction between simple control and reliable performance
Solution Approach 2:
The system dynamically changes the duty ratio parameter based on the detected power-supply voltage magnitude. When voltage varies, the duty ratio is adjusted accordingly to maintain constant motor acceleration, transforming a static control approach into a dynamic adaptive control that resolves the acceleration consistency issue
2Productivity
If the duty ratio is increased rapidly to achieve quick motor startup, then the productivity is improved, but the motor acceleration becomes excessive and causes operational inconsistencies
Solution Approach 1:
The control circuit dynamically adjusts the duty ratio increase rate based on the detected power-supply voltage magnitude. For higher voltages, the duty ratio increases more slowly; for lower voltages, it increases more rapidly. This dynamic adaptation ensures consistent motor acceleration and operational reliability while maintaining high productivity
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 effectively reduces variations in motor acceleration and rotational speed due to power-supply voltage fluctuations, enhancing operational consistency.
Implementation Method 1
a voltage detector configured to detect a magnitude of the power-supply voltage
Implementation Method 2
The drive circuit is configured to apply the power-supply voltage to the motor in accordance with the first duty ratio to thereby drive the motor
Data Source
AI summary
One aspect of the present disclosure provides an electric power tool including a motor, a drive circuit, a voltage detector, a first calculator, and a second calculator. The drive circuit applies a power-supply voltage to the motor in accordance with a first duty ratio. The voltage detector detects a magnitude of the power-supply voltage. The first calculator calculates a desired duty ratio based on the magnitude of the power-supply voltage detected. The second calculator increases the first duty ratio from an initial value to the desired duty ratio in accordance with a lapse of time. The second calculator varies a rate of increase of the first duty ratio based on the magnitude of the power-supply voltage detected.