Electric Tool PWM Control for Smooth Speed Under Battery Voltage Drop
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Solution Overview
Problem
Conventional electric tools experience abrupt changes in motor speed due to voltage fluctuations, leading to instability, as they rely on look-up tables with large voltage ranges that result in sudden changes when shifting between voltage ranges.
Innovation Solution
The electric tool employs a controller that uses regression equations, such as polynomial, exponential, or logarithmic functions, to calculate duty ratios for pulse-width modulation signals, allowing for smoother motor speed control by continuously adjusting the duty ratio as battery voltage decreases, thereby maintaining stable rotational speed across different voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a look-up table with large voltage ranges is used to control motor speed, then the device complexity is reduced, but the motor speed stability deteriorates due to abrupt changes when shifting between voltage ranges
Solution Approach 1:
The patent changes the control parameter from discrete voltage range thresholds to continuous polynomial function coefficients. By using polynomial equations with dynamically adjusted coefficients based on battery voltage, the system achieves smooth motor speed control without abrupt transitions, resolving the stability issue while maintaining manageable complexity through algorithmic control.
Solution Approach 2:
The patent transitions from a static look-up table approach to a dynamic polynomial-based control system. The control parameters (duty ratios) are dynamically calculated using polynomial functions that adapt to changing battery voltage, enabling continuous adjustment and eliminating the abrupt transitions inherent in fixed voltage range thresholds.
2Stability of the object's composition
If the voltage ranges in the look-up table are made smaller to improve motor speed smoothness, then the motor speed stability improves, but the device complexity increases due to more detailed voltage range segmentation
Solution Approach 1:
Instead of increasing the number of voltage ranges, the patent changes the fundamental approach by using polynomial function coefficients as control parameters. This allows continuous adjustment of duty ratios based on battery voltage without requiring fine-grained voltage range segmentation, achieving smooth control without increased complexity.
Solution Approach 2:
The patent replaces the mechanical look-up table structure with a mathematical polynomial-based control system. This substitution eliminates the need for discrete voltage range thresholds and associated complexity, using continuous mathematical functions to achieve smooth motor speed control across the entire voltage range.
3Stability of the object's composition
If polynomial regression equations are used to calculate duty ratios, then the motor speed smoothness improves through continuous adjustment, but the computational complexity increases
Solution Approach 1:
The patent performs preliminary calculations by pre-determining polynomial regression coefficients through offline regression analysis. These pre-calculated coefficients are stored in the controller, eliminating the need for real-time complex computations during motor operation. The controller only needs to evaluate simple polynomial expressions with pre-computed coefficients, achieving smooth control with minimal computational burden.
Solution Approach 2:
The patent implements dynamic coefficient adjustment based on battery voltage ranges. By dividing the voltage range into segments and assigning different polynomial coefficients to each segment, the system achieves adaptive smooth control without requiring computationally intensive real-time optimization. This dynamic segmentation approach balances computational efficiency with control smoothness.
Data Source
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AI summary
A method of controlling a rotational speed of an electric tool is provided. The electric tool includes a battery (21), a battery voltage detection circuit (41), a motor unit (3), and a controller (6). The controller (6) stores at least one regression equation of duty ratio on voltage, and detects a voltage of the battery (21) through the battery voltage detection circuit (41). The controller (6) obtains a duty ratio for a control signal by substituting the voltage of the battery (21) into the at least one regression equation, and outputs the control signal with the duty ratio obtained from the at least one regression equation to the motor unit (3) for controlling operation of the motor unit (3).