Off-Axis Multi-Turn Position Sensing Without Mechanical Gear Trains
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Solution Overview
Problem
Existing technologies face challenges in accurately determining the absolute angle position and turn count of rotatable components, such as steering wheel shafts and cam shafts, often requiring complex gear trains and lacking efficient, cost-effective, and compact position sensing solutions.
Innovation Solution
An off-axis multi-turn position measurement system utilizing a magnet with a spiral or helical pattern of magnetized poles and off-axis magnetic field sensors, including an angle position sensor and a multi-turn magnetoresistive sensor, to determine angle position and turn count without physical contact, enabling compact and reliable measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex gear trains are used to determine absolute angle position and turn count, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent replaces mechanical gear trains with a magnetic field-based sensing system. A magnet with spiral or helical magnetization pattern generates a magnetic field that varies with rotation, which is detected by off-axis magnetic field sensors. This substitution eliminates mechanical complexity while maintaining measurement capability for both absolute angle position and turn count.
Solution Approach 2:
The patent introduces a magnetic field as an intermediary between the rotatable component and the sensing system. The magnet converts mechanical rotation into magnetic field variations, which the off-axis sensors then detect. This intermediary approach enables non-contact measurement and simplifies the overall system architecture.
2Reliability
If non-contact sensing is implemented, then reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs off-axis sensor positioning rather than concentric alignment. The sensors are positioned at a specific offset distance from the rotation axis, creating an asymmetric measurement geometry. This asymmetric configuration provides inherent tolerance to air gap variations and misalignment, reducing manufacturing precision requirements while maintaining reliable non-contact sensing.
Solution Approach 2:
The patent utilizes the spatial variation of magnetic field parameters (strength and direction) at off-axis positions. By positioning sensors off-axis, the system exploits the specific magnetic field gradient characteristics in that region, which provides robust measurement signals that are less sensitive to manufacturing tolerances and air gap variations.
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 system provides accurate, non-contact sensing with improved packaging, redundancy, and reduced cost by eliminating the need for complex gear trains, offering enhanced measurement accuracy and scalability.
Implementation Method 1
the magnet generates a magnetic field having varying magnetic field direction based on the spiral pattern of the magnet
Implementation Method 2
a multi-turn magnetoresistive sensor configured to generate the second output
Data Source
AI summary
Various embodiments are directed to an off-axis multi-turn position measurement system comprising a magnet defining a magnetic surface comprising at least two magnetized poles arranged in a spiral pattern and an opening for receiving a rotatable component; and at least one magnetic field sensor assembly positioned proximate to the magnetic surface such that the at least one magnetic field sensor assembly is off-axis with respect to a center axis defined by the magnet. The magnet may be rotatable about the center axis relative to the at least one magnetic field sensor, the at least one multi-turn magnetic field sensor may be configured to generate at least a first output and a second output based on the magnetic field, and an angle position and turn count of the rotatable component may be determined based on the first output and the second output respectively.