Power Tool Motor Speed Control via Load Estimation
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Solution Overview
Problem
Current power tools, such as electric lawnmowers, face inefficiencies in maintaining optimal rotational speed under varying loads, as they either reduce speed with increased load or increase speed with decreased load, failing to meet user demands for higher speed in dense conditions and lower speed in sparse conditions.
Innovation Solution
A power tool with an electric motor, detection device, and controller that estimates a load parameter from the duty cycle and rotational speed, allowing the motor to operate at a lower speed under lower loads and higher speed under higher loads by adjusting the duty cycle of the control signal, enabling constant speed modes to match actual working conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a constant duty cycle is used to control the electric motor, then the control system is simple, but the rotational speed varies with load changes which does not meet user requirements
Solution Approach 1:
The patent implements dynamic speed adjustment by switching between multiple predetermined speed levels (first, second, third speeds) based on detected load changes. The controller dynamically adjusts the duty cycle to maintain appropriate speed under varying load conditions, transforming the static constant-duty-cycle approach into a dynamic adaptive control system.
Solution Approach 2:
The patent employs feedback control by detecting the actual rotational speed or load conditions and using this information to adjust the duty cycle. The controller continuously monitors system state and modifies the control signal accordingly, creating a closed-loop control system that maintains optimal speed despite load variations.
2Productivity
If the rotational speed is increased under higher load, then the cutting performance improves, but the energy consumption increases
Solution Approach 1:
The system dynamically adjusts speed based on actual load conditions rather than maintaining a constant high speed. When load increases (detected through current sensing or speed deviation), the controller increases speed to maintain cutting efficiency. When load decreases, the controller reduces speed to minimize energy consumption, creating an adaptive energy-efficient operation mode.
Solution Approach 2:
The patent changes the operational parameters (speed levels, duty cycle values) based on detected load conditions. By having multiple predetermined speed levels and switching between them according to load, the system optimizes the balance between productivity and energy consumption for different operating conditions.
Data Source
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AI summary
A power tool includes an electric motor, a functional accessory capable of being driven by the electric motor, a detection device for detecting a rotational speed of the electric motor, and a controller for controlling the electric motor with a control signal. The control is operable to estimate a load parameter according to a duty cycle of the control signal and the rotational speed of the electric motor such that the electric motor is caused to be operated by the controller with a lower rotational speed under a lower load and a higher rotational speed under a higher load.