Power Tool Motor Restart Control Using Variable Duty Cycles
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Solution Overview
Problem
Power tools face inefficiencies and user experience issues due to the need for quick restarts, as they often require complete shutdown and subsequent restart, which can be time-consuming and affect working efficiency, especially in scenarios like changing blowing angles with electric blowers or cutting tools.
Innovation Solution
A power tool design incorporating a control circuit with a driver circuit and controller that detects working parameters to output control signals with variable duty cycles, allowing for smooth and rapid restarts within a preset time frame, even before complete shutdown, by converting braking torque into starting torque and managing freewheeling states to reduce heat and improve efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power tool is completely shut down and then restarted, then the motor can be fully stopped and controlled, but the restart time increases and working efficiency decreases
Solution Approach 1:
The control circuit begins reducing the duty cycle of the control signal before the shutdown command is fully executed, preparing the motor for smooth cessation and rapid restart. The controller starts adjusting the duty cycle in advance based on the shutdown detection, allowing the motor to be pre-conditioned for quick restart without complete stopping.
Solution Approach 2:
The duty cycle is dynamically adjusted during the shutdown and restart process rather than using fixed on/off control. The controller continuously modifies the duty cycle based on real-time motor state and shutdown timing, enabling smooth transition between operating states and reducing restart time while maintaining control stability.
2Loss of time
If the duty cycle is adjusted during shutdown, then the restart time is reduced, but the control circuit complexity increases
Solution Approach 1:
The existing controller that already outputs control signals to the motor is extended to also perform duty cycle adjustment during shutdown. The same control circuit handles both normal motor control and shutdown management functions, avoiding the need for separate dedicated shutdown control hardware and reducing overall system complexity.
Solution Approach 2:
The controller modifies the duty cycle parameter of the existing control signal to achieve smooth shutdown and rapid restart. By changing the duty cycle from 100% to 0% gradually during shutdown and vice versa during restart, the system achieves time reduction using parameter adjustment rather than additional control mechanisms.
3Reliability
If the motor brakes completely before restart, then the motor is fully stopped, but the braking time extends and operational continuity is reduced
Solution Approach 1:
The control circuit begins reducing the duty cycle before the shutdown command is fully executed, preparing the motor for smooth cessation and rapid restart. The controller starts adjusting the duty cycle in advance based on the shutdown detection, allowing the motor to be pre-conditioned for quick restart without complete stopping.
Solution Approach 2:
The motor maintains a low-level operational state during shutdown rather than complete stopping, keeping the motor in a ready state that can quickly transition back to full operation. This continuous low-level action preserves operational readiness and reduces the time needed to resume full working state.
Data Source
AI summary
A power tool includes an operating switch; a motor that is connected to the operating switch and capable of starting in response to the conduction of the operating switch and braking in response to the disconnection of the operating switch; and a control circuit configured to control a working state of the motor. The control circuit includes a driver circuit including multiple switching elements; a controller that is coupled to the motor and capable of outputting a first control signal to control the motor to start; and a parameter detection unit for detecting a working parameter of the motor. The controller is configured to, in response to the operating switch being turned on again within a preset time after being turned off, acquire the working parameter and set a duty cycle of a second control signal according to the working parameter to control the motor to restart.