Power Tool Start-Up Control With Temperature-Adaptive Speed Ramp
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Solution Overview
Problem
Existing power tools face challenges in efficiently starting up the electric motor due to internal mechanical loads, which can lead to slow acceleration and potential failure if the rotational speed ramp is too steep.
Innovation Solution
The control unit of the power tool adjusts the slope of the rotational speed ramp and the current strength of the motor current based on detected temperature, allowing the electric motor to adapt to varying internal mechanical loads and start up more quickly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotational speed ramp is designed steep to reduce start-up time, then productivity is improved, but reliability deteriorates because the rotor cannot follow the electric field and the motor fails to start
Solution Approach 1:
The patent applies dynamics by making the rotational speed ramp adaptive rather than fixed. The control unit continuously monitors the actual rotational speed of the rotor and dynamically adjusts the slope of the rotational speed ramp during start-up. This allows the system to optimize between fast start-up (steep ramp) and reliable tracking (flat ramp) based on real-time conditions, resolving the contradiction between productivity and reliability.
2Reliability
If the rotational speed ramp is designed flat to ensure the rotor can follow the electric field, then reliability is improved, but productivity deteriorates because the start-up mode takes longer
Solution Approach 1:
The patent implements feedback control by continuously measuring the actual rotational speed of the rotor during start-up and using this information to adjust the rotational speed ramp. The control unit compares the actual speed with the target ramp profile and modifies the ramp slope accordingly. This feedback mechanism allows the system to maintain reliability while minimizing start-up time, as the ramp adapts to the actual motor response rather than following a predetermined conservative profile.
3Reliability
If the rotational speed ramp is designed for the worst case (greatest internal mechanical load), then reliability is improved, but productivity deteriorates under lighter load conditions due to unnecessarily long start-up time
Solution Approach 1:
The patent makes the rotational speed ramp dynamic and adaptive to actual load conditions. Instead of using a fixed conservative ramp designed for worst-case scenarios, the control unit continuously monitors motor performance and adjusts the ramp slope in real-time. This allows the system to achieve fast start-up under light loads while maintaining reliability under heavy loads, as the ramp profile adapts to the actual mechanical load present during each start-up event.
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 the power tool to start up more efficiently, reducing the time required to reach the working rotational speed, especially under conditions with lower internal mechanical loads.
Implementation Method 1
the control unit continuously increases the frequency of the motor current to achieve the continuous increase in the rotational speed of the electric motor
Implementation Method 2
The power tool is controlled from the time the working rotational speed is reached preferably using a sensorless principle, in particular using a Back-EMF principle
Data Source
AI summary
A power tool, in particular a handheld power tool, for example a grinding machine, that includes a tool, an electric motor for driving the tool, and a control unit for actuating the electric motor using a motor current (MI). The control unit has a start-up mode in which the control unit actuates the electric motor in such a way that the electric motor during the start-up mode traverses a rotational speed ramp (DR), at which the rotational speed of the electric motor is increased continuously up to operating rotational speed (ADZ) The control unit 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 the acquired temperature for the start-up mode.