Power Tool Start-Up Control Using Temperature-Adaptive Speed Ramps
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Solution Overview
Problem
Existing power tools face challenges in efficiently starting up due to varying internal mechanical loads, which can lead to slow acceleration and potential failure if the speed ramp is too steep, and require a flat speed ramp to ensure motor followability, resulting in longer start-up times.
Innovation Solution
The power tool's control unit adjusts the motor current intensity and the gradient of the speed ramp based on detected temperature, allowing for dynamic adaptation to the internal mechanical load, thereby optimizing start-up speed without requiring a flat speed ramp.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a steep speed ramp is used during start-up, then the start-up time is reduced, but the rotor may fail to follow the electric field causing start-up failure
Solution Approach 1:
The patent implements dynamic adjustment of the speed ramp gradient during the start-up phase. The control unit continuously monitors the actual rotor speed and compares it with the reference speed ramp, dynamically modifying the gradient to ensure the rotor can follow the electric field while minimizing start-up time. This resolves the contradiction by making the speed ramp adaptive rather than fixed.
Solution Approach 2:
The patent employs feedback control by measuring the actual rotor speed during start-up and using this information to adjust the motor current and speed ramp gradient. The control unit modifies the reference speed ramp based on the deviation between actual and reference speeds, ensuring reliable start-up while optimizing time. This feedback mechanism allows the system to respond to real-time conditions and prevent start-up failure.
2Reliability
If a flat speed ramp is used during start-up, then the rotor can reliably follow the electric field, but the start-up time increases
Solution Approach 1:
The patent transitions from a static flat speed ramp to a dynamic speed ramp that adjusts its gradient based on real-time rotor speed feedback. This allows the system to maintain reliability by ensuring the rotor follows the electric field while reducing unnecessary conservatism, thereby optimizing start-up time without sacrificing reliability.
Solution Approach 2:
The patent changes the parameters of the speed ramp dynamically during start-up. The control unit adjusts the gradient of the speed ramp based on the actual rotor speed and temperature conditions, transforming the fixed parameter approach into a variable parameter approach that optimizes both reliability and time efficiency.
3Adaptability or versatility
If the speed ramp is designed for the worst-case scenario (highest internal mechanical load), then the motor can execute the speed ramp under all conditions, but the start-up time is prolonged
Solution Approach 1:
The patent introduces temperature-dependent parameter changes to the speed ramp design. Based on the detected temperature and estimated internal mechanical load, the control unit adjusts the speed ramp gradient and motor current intensity. This allows the system to adapt to different load conditions rather than always using the worst-case parameters, thereby reducing start-up time when full load is not present while maintaining adaptability.
Solution Approach 2:
The patent makes the speed ramp dynamic and adaptive to actual operating conditions. Instead of using a fixed speed ramp designed for worst-case scenarios, the system continuously adjusts the speed ramp parameters based on real-time temperature and load estimates, enabling optimal performance across varying conditions without always incurring the penalty of prolonged start-up time.
4Speed
If the motor current intensity is increased during start-up, then the acceleration is improved, but the heat generation increases which may affect motor performance
Solution Approach 1:
The patent implements temperature-dependent parameter changes to the motor current intensity. The control unit adjusts the current magnitude based on the detected temperature and estimated internal mechanical load. This allows the system to optimize acceleration while managing heat generation, as the current is increased only when temperature conditions permit, thereby balancing speed improvement with thermal management.
Solution Approach 2:
The patent employs feedback control by monitoring temperature and using this information to adjust the motor current intensity during start-up. The control unit modifies the current profile based on thermal conditions, ensuring that acceleration is optimized without excessive heat generation that could compromise motor performance or safety.
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 approach enables faster start-up times by adjusting the speed ramp and motor current intensity according to the temperature-dependent internal mechanical load, improving the power tool's responsiveness and efficiency.
Implementation Method 1
The internal mechanical load—specifically, the moment of inertia—which counteracts the drive of the tool is temperature-dependent
Implementation Method 2
an electric motor for driving the tool, and a control unit for controlling the electric motor with a motor current
Data Source
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AI summary
The invention relates to a power tool (2), in particular a handheld power tool, for example a grinding machine, comprising a tool (5), an electric motor (6) for driving the tool (5), and a control unit (7) for actuating the electric motor (6) using a motor current (MI), wherein the control unit (7) has a start-up mode in which the control unit (7) actuates the electric motor (6) in such a way that the electric motor (6) during the start-up mode traverses a rotational speed ramp (DR), at which the rotational speed of the electric motor (6) is increased continuously up to an operating rotational speed (ADZ), wherein the control unit (7) is designed to adjust the gradient of the rotational speed ramp (DR) on the basis of an acquired temperature for the start-up mode and/or to adjust the intensity of the motor current (MI) on the basis of a/the acquired temperature for the start-up mode.