Inductive Position Sensor Triple Coil Compensation
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Solution Overview
Problem
Inductive position or angle measuring devices face challenges such as space constraints, temperature dependency, mechanical tolerances, and interference from metal sludge in gear transmissions, which affect their accuracy and reliability in a wide temperature range and under varying mechanical conditions.
Innovation Solution
An inductive position or angle measuring device using LC tank circuits with independently operating oscillators, a reference coil to compensate for interference, and a digital evaluation circuit that processes pulse frequencies directly, eliminating the need for analog/digital converters and separate clock generators, and utilizing a triple coil arrangement to minimize space and enhance linear measurement range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If inductive measuring devices are used in gear transmissions, then position or angle measurement can be achieved, but temperature dependency and mechanical tolerances affect measurement accuracy
Solution Approach 1:
The patent employs feedback by continuously monitoring the oscillation frequencies of both measuring and reference oscillators and using these signals to compensate for temperature and mechanical tolerance effects. The evaluation circuit processes the frequency differences to determine actual position while correcting for environmental variations.
Solution Approach 2:
The patent changes the operating parameters by using variable oscillation frequencies that adapt to temperature and mechanical conditions. The measuring and reference oscillators are designed to operate at frequencies that shift with temperature, allowing the system to maintain accuracy through frequency-based compensation rather than fixed parameter operation.
2Measurement precision
If inductive measuring devices are used in gear transmissions, then position or angle measurement can be achieved, but metal sludge interference reduces reliability
Solution Approach 1:
The patent introduces an intermediary reference oscillator that is shielded from metal sludge interference and serves as a reference signal. This reference oscillator acts as a mediator between the measuring oscillator and the evaluation circuit, allowing the system to distinguish between position-induced frequency changes and those caused by metal sludge interference.
Solution Approach 2:
The patent converts the harmful effect of metal sludge interference into a beneficial reference signal. By designing the reference oscillator to be equally affected by metal sludge as the measuring oscillator, the system uses the interference itself as a reference point, allowing the evaluation circuit to subtract out the interference and extract the true position information.
3Measurement precision
If traditional oscillator circuits with separate clock generators and analog/digital converters are used, then frequency measurement can be achieved, but device complexity and space requirements increase
Solution Approach 1:
The patent merges the clock generator function with the oscillator circuits themselves. The oscillators directly produce the frequency signals that serve as both the measurement signal and the reference signal, eliminating the need for separate clock generators. The evaluation circuit also integrates the analog-to-digital conversion function, combining multiple functions into a single compact unit.
Solution Approach 2:
The patent implements multi-functionality by designing the oscillators to serve multiple purposes: they generate the measurement signal, provide the reference signal, and their frequency outputs directly feed into the evaluation circuit for both position determination and temperature compensation. The evaluation circuit itself performs multiple functions including frequency measurement, position calculation, and environmental compensation.
4Ease of manufacture
If planar coils are used on printed circuit boards, then manufacturing ease is improved, but mechanical tolerances affect the distance to the measuring element
Solution Approach 1:
The patent uses parameter changes by making the oscillation frequencies sensitive to distance variations. When mechanical tolerances cause distance changes between the planar coils and the measuring element, the oscillation frequencies shift accordingly. The evaluation circuit detects these frequency shifts and compensates for the distance variations, maintaining measurement accuracy despite manufacturing tolerances.
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
The solution provides a space-saving, temperature-insensitive, and mechanically tolerant position or angle measuring device with high positional accuracy and a wide linear measurement range, capable of compensating for mechanical and thermal variations, and resistant to interference from metal sludge.
Implementation Method 1
The magnetic field of the measuring coil generates eddy currents in an electrically conductive measuring element, which react on the coil. Among other things, the inductance of the measuring coil is influenced by the spatial position of the measuring element relative to the coil.
Implementation Method 2
The inductive measuring device preferably works according to the principle of the eddy current sensor... The magnetic field of the measuring coil generates eddy currents in an electrically conductive measuring element
Data Source
Figure 1a~1c
Figure 2
Figure 3~4
AI summary
The device has a measuring oscillator with a measuring coil changing a pulse frequency of the oscillator based on inductance changes produced by a movable measuring unit depending on an overlapping rate between the coil and the unit. A measuring-or reference oscillator has a measuring-or reference coil that is defined to either completely cover or uncover the reference coil by the unit, so that a pulse frequency of the reference oscillator does not depend on the rate. The frequencies are counted and set in a digital evaluation circuit e.g. application specific integrated circuit (ASIC).