Power Tool Rotor Position Detection Before Magnetic Saturation
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Solution Overview
Problem
Existing methods for determining the rotor position of electric motors in power tools, such as electric screwdrivers, face challenges due to magnetic saturation, which impairs the reliability of current-based detection methods, often requiring oversized motors to prevent saturation and thus limiting efficiency.
Innovation Solution
A method that checks if the electric motor current is below a threshold value to ensure no magnetic saturation, allowing for reliable rotor position detection without sensors by operating the motor in distinct phases for position determination and torque generation, ensuring detection occurs before saturation occurs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric motor is dimensioned large to prevent magnetic saturation, then magnetic saturation is avoided and rotor position detection is reliable, but the motor size increases and efficiency decreases
Solution Approach 1:
The patent applies preliminary action by performing rotor position detection during a pre-phase before the motor enters the torque phase where magnetic saturation would occur. The control unit detects rotor position while the motor is still in the pre-phase with lower current, before switching to the torque phase with higher current that would cause saturation. This timing-based separation allows reliable detection without requiring oversized motors.
Solution Approach 2:
The patent implements dynamics by dynamically switching between two operational phases: a pre-phase for rotor position detection with lower current to avoid saturation, and a torque phase for power delivery with higher current. The control unit transitions the motor between these phases based on detection needs, allowing the motor to operate efficiently at normal size while maintaining detection reliability through phase-based dynamic operation.
2Power
If the electric motor current is increased for torque generation, then power output improves, but magnetic saturation occurs and rotor position detection becomes unreliable
Solution Approach 1:
The patent applies segmentation by dividing motor operation into distinct phases: a pre-phase for rotor position detection with lower current, and a torque phase for power delivery with higher current. The control unit separates these functions temporally, ensuring detection occurs during the pre-phase before saturation-level currents are applied in the torque phase. This phase segmentation resolves the conflict between power output and detection reliability.
Solution Approach 2:
The patent implements periodic action by repeatedly cycling between pre-phase detection periods and torque phase power delivery periods. The control unit periodically switches to the pre-phase to perform rotor position detection, then returns to the torque phase for power output, creating a rhythmic pattern of detection and power delivery that maintains both reliability and performance.
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
Enables efficient and reliable rotor position detection in power tools, preventing impairment from magnetic saturation and allowing for smaller motor designs, thus enhancing operational efficiency and tool performance.
Implementation Method 1
checking whether a first electric motor current I1 is below a threshold value SW... When the electric motor is magnetically saturated, the dependence of the winding inductance on the rotor position is generally very low or no longer present.
Data Source
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AI summary
The invention relates to a method for determining a rotor position of an electric motor (2) of a power tool (10), in particular of a screwdriving power tool, comprising the steps: testing (S4) whether a first electric motor current (I1) is below a threshold value (SW), and, in response to the testing showing that the first electric motor current (I1) is below the threshold value (SW), determining a rotor position of the electric motor (2) on the basis of the first electric motor current (I1) and/or a second electric motor current.