Archimedean Spiral Encoder for Compact Rotation Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing systems for determining rotation parameters of rotating members face challenges in achieving precise measurements with a compromise between sinusoidality and amplitude of the magnetic signal, particularly with a low number of pole pairs, leading to issues with signal detection and integration in reduced dimensions.
Innovation Solution
A system comprising an encoder with a magnetic track featuring alternating North and South poles along an Archimedean spiral, and a rotation sensor with sensitive elements positioned at an optimal angle to deliver signals in quadrature, allowing for independent selection of pole pairs and pole width, thereby improving precision and signal quality without increasing encoder thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of pole pairs is reduced to less than 6, then the pole width becomes large (order of ten millimeters), but the sinusoidality of the magnetic signal deteriorates and the reading gap must be increased, which reduces signal amplitude
Solution Approach 1:
The patent applies an Archimedean spiral geometry to the magnetic track, replacing traditional circular or linear patterns. This curved spiral configuration allows the magnetic poles to be distributed along a spiral path defined by r = a + bθ, creating a geometric progression that maintains consistent pole spacing and signal characteristics even with fewer pole pairs, thereby preserving signal quality while reducing the number of poles
Solution Approach 2:
The patent changes the geometric parameters of the magnetic track by introducing the Archimedean spiral equation with specific constants (a and b) that control the spiral's tightness and pole distribution. By optimizing these parameters, the system achieves adequate signal sinusoidality and amplitude with fewer pole pairs, resolving the contradiction between pole count and signal quality
2Adaptability or versatility
If the pole width is increased to accommodate fewer pole pairs, then the encoder thickness must be increased to preserve sinusoidality, but this complicates magnetization and reduces integration feasibility
Solution Approach 1:
The Archimedean spiral geometry inherently distributes magnetic flux more evenly through its expanding radial pattern, which maintains signal sinusoidality without requiring increased encoder thickness. The spiral's geometric progression allows the magnetic field to traverse a longer effective path within the same radial space, preserving signal quality while keeping the encoder compact
Solution Approach 2:
The patent transitions from a traditional circular pole arrangement to a spiral configuration that utilizes the angular dimension more effectively. By distributing poles along a spiral path that expands radially, the system achieves equivalent magnetic signal quality with reduced thickness, as the spiral geometry optimizes the three-dimensional distribution of magnetic flux
3Measurement precision
If sensitive elements are positioned closer to the magnetic track to improve signal amplitude, then mechanical interaction risks increase, but positioning them farther away reduces signal amplitude
Solution Approach 1:
The Archimedean spiral geometry creates a magnetic field distribution that maintains consistent field strength along the spiral path. This geometric configuration allows the magnetic flux to remain sufficiently strong at moderate reading distances, enabling the sensor to be positioned at a safe distance (avoiding mechanical contact) while still detecting adequate signal amplitude through the optimized spiral field pattern
4Measurement precision
If the encoder height is increased to accommodate adequate pole width and sensor positioning, then integration constraints are violated, but reducing height compromises signal quality
Solution Approach 1:
The Archimedean spiral geometry optimizes the use of radial space by distributing magnetic poles along an expanding spiral path. This configuration achieves adequate pole width and signal quality within a compact radial envelope, allowing the encoder to maintain a small height (less than 6.Lp) while preserving measurement precision through the efficient geometric arrangement of the magnetic track
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 enhances the accuracy of rotation parameter determination, reduces edge effects, and allows for efficient signal processing, including effective filtering of harmonics, while maintaining a compact encoder design.
Implementation Method 1
an encoder emitting a periodic magnetic signal as well as a rotation sensor capable of detecting said magnetic field
Implementation Method 2
each sensitive element can comprise at least one pattern based on a magnetoresistive material with tunnel effect (TMR in English for Tunnel Magneto Resistance) whose resistance varies according to the detected magnetic field
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a system comprising: an encoder (1) whose magnetic track (2) has an alternation of North and South magnetic poles separated by i Archimedean spiral transitions (3); a rotation sensor capable of detecting the periodic magnetic field emitted by said encoder by means of several sensitive elements (4a, 4b) distributed angularly along the magnetic track (2) to deliver each a signal representative of the rotation of the encoder (1), said sensor further comprising a device for subtracting the signals (V1, V2) delivered by two sensitive elements (4a, 4b) forming between them an angle γ which is such that: 0.55π < γ.Npp < 0.83π, modulo 2π or 1.17π < γ.Npp < 1.45π, modulo 2π.