Inductive Rotation Angle Sensor Immune to Magnetic Interference
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Solution Overview
Problem
Existing rotation angle sensors are susceptible to external disturbances and installation tolerances, particularly in environments with high electromagnetic interference, such as the engine compartment of a vehicle, which affects the accuracy of measuring the rotation angle between a shaft and another component.
Innovation Solution
A rotation angle sensor comprising a stator element with at least three coils and a rotatably mounted rotor element that inductively couples differently with each coil based on the rotation angle, along with an evaluation unit that supplies the coils cyclically with AC voltage to induce voltages in other coils, allowing precise determination of the angle by measuring the phase and magnitude of induced AC voltages, and compensating for external interference by using coils with opposite turns and overlapping configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnet and magnetic field sensor are used to measure rotation angle, then the rotation angle can be determined, but the sensor becomes susceptible to external magnetic fields and interference
Solution Approach 1:
The patent replaces the magnetic field-based measurement system with an inductive coupling system using coils and a conductive target. Instead of measuring magnetic field vectors directly, the system uses electromagnetic induction where the conductive target modulates the inductance of excitation coils, and receiving coils detect the induced voltages. This substitution eliminates susceptibility to external magnetic fields while maintaining rotation angle measurement capability.
Solution Approach 2:
The patent introduces a conductive target as an intermediary element between the excitation coils and receiving coils. This target modulates the electromagnetic coupling indirectly through its position-dependent effect on inductance, rather than directly sensing magnetic fields. The intermediary target converts rotational position into inductance modulation, which is then detected by the receiving coils, providing immunity to external magnetic interference.
2Measurement precision
If eddy current effect with metallic target and sensor coils is used, then rotation angle can be determined via frequency change, but the sensor exhibits high lateral sensitivity to installation tolerances and is disrupted by external electromagnetic fields
Solution Approach 1:
The patent divides the single-coil eddy current sensor into multiple separate coils: excitation coils and receiving coils. This segmentation allows the system to separate the function of generating the electromagnetic field from detecting the modulated signal. The receiving coils detect voltages induced by the conductive target's position without being directly affected by external electromagnetic fields at their operating frequency, reducing lateral sensitivity and electromagnetic disruption.
Solution Approach 2:
The patent uses periodic excitation of the coils with alternating current to generate time-varying magnetic fields that induce voltages in the receiving coils. By measuring the amplitude and phase of these periodically induced voltages, the system determines rotation angle. This periodic action at controlled frequencies allows filtering and signal processing to reject external electromagnetic interference that does not match the excitation frequency.
3Measurement precision
If coupled coils with alternating electromagnetic field are used, then rotation angle can be determined, but external disturbances still affect the measurement
Solution Approach 1:
The patent implements a measurement system where receiving coils detect voltages induced by the conductive target's position-dependent coupling with excitation coils. The evaluation unit processes these induced voltage signals to determine rotation angle. This feedback mechanism continuously monitors the inductive coupling state and compensates for external disturbances by comparing expected versus actual coupling characteristics, maintaining measurement accuracy despite external interference.
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 solution significantly reduces the influence of external disturbances and component tolerances, enabling precise determination of the rotation angle with improved accuracy and robustness against electromagnetic interference, particularly in harsh environments.
Implementation Method 1
an alternating electromagnetic field is generated in a single excitation coil, which couples to several receiving coils and induces a voltage in each
Implementation Method 2
a rotor element rotatably mounted with respect to the stator element and configured to couple inductively with each of the at least three coils to varying degrees depending on the rotation angle
Data Source
Figure 1~2
Figure 3A~3B
Figure 3C~4
AI summary
An angular position sensor (10) comprises a stator element (12) having at least three coils (20); a rotor element (14) mounted for rotation with respect to the stator element (12), and which is configured to inductively couple with each of the at least three coils (20) with varying strength according to an angle of rotation; and an evaluation unit (22) for determining the angle of rotation between the rotor element (14) and the stator element (12). The evaluation unit (22) is configured to supply the coils (20) with alternating voltage in a cyclical manner and in sequence, so that a first respective part of the coils (20) is supplied with alternating voltage and a remaining part is de-energized via the evaluation unit; and, in a cyclical manner in sequence in one or more de-energized coils (20), to detect a respective phase and/or an amount of an induced alternating voltage and to determine the angle of rotation from same.