Eddy Current Encoder Scale With Varying Recess Depths
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Solution Overview
Problem
Existing absolute position encoders, particularly those using optical, capacitive, and magnetic technologies, are sensitive to contamination by particles such as ferromagnetic particles, oil, and water, making them impractical for use in manufacturing environments without expensive environmental seals, and they often require additional components for incremental and absolute position measurements.
Innovation Solution
A position sensing device utilizing an eddy current transducer with a scale pattern featuring alternating first and second scale element zones, where the second scale element zones have varied characteristics to provide distinct eddy current responses, allowing a single read head to output both incremental and absolute position signals, thus eliminating the need for a second scale track and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical, capacitive, or magnetic transducers are used for position measurement, then measurement capability is provided, but sensitivity to contamination makes them impractical for manufacturing environments
Solution Approach 1:
The patent replaces optical, capacitive, or magnetic transduction mechanisms with an eddy current-based inductive transducer system. The read head generates an oscillating magnetic field that induces eddy currents in the conductive scale, and the resulting impedance changes are detected to determine position. This substitution provides inherent immunity to contamination by particles, oil, water, and other fluids, making the system suitable for manufacturing environments where previous technologies failed.
2Adaptability or versatility
If a second scale track is added to provide both incremental and absolute position measurements, then measurement functionality is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent makes the single scale track universal by varying the characteristics of scale elements to encode both incremental and absolute position information. The scale includes first scale elements with uniform characteristics for incremental measurement and second scale elements with varying characteristics (different heights, widths, or conductive properties) that encode absolute position. This multi-functionality eliminates the need for a separate second scale track, reducing device complexity while maintaining both measurement capabilities.
Solution Approach 2:
The patent applies local quality by making different portions of the same scale track have different characteristics. Specifically, the scale includes regions with first scale elements having uniform properties and regions with second scale elements having varied properties (different heights, widths, or conductive characteristics). This local differentiation allows a single read head to distinguish between incremental and absolute position information without requiring separate scale tracks, thereby reducing overall device complexity.
3Adaptability or versatility
If multiple scale tracks are used for comprehensive position measurement, then measurement capability is enhanced, but power consumption increases
Solution Approach 1:
The patent makes the single scale track universal by varying the characteristics of scale elements to encode both incremental and absolute position information. The scale includes first scale elements with uniform characteristics for incremental measurement and second scale elements with varying characteristics (different heights, widths, or conductive properties) that encode absolute position. This multi-functionality eliminates the need for a second scale track, reducing device complexity while maintaining both measurement capabilities.
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 compact, high-resolution, cost-effective, and robust position sensing device that is immune to contamination, capable of determining both incremental and absolute positions with a single read head, reducing the need for additional components and power consumption.
Implementation Method 1
a read head movable relative to the scale pattern along the measuring axis direction and including an excitation portion that excites the eddy currents in the scale pattern
Implementation Method 2
an excitation portion that excites the eddy currents in the scale pattern and a signal portion that outputs position signals that vary depending on the eddy currents
Data Source
AI summary
An absolute position encoder scale is provided having scale elements (e.g., plates and plate abatement features such as recesses) which alternate along the scale pattern. At least one of the scale elements has a characteristic (e.g., a recess depth) that is varied along the scale pattern to provide a different respective eddy current response. A signal portion of a read head is responsive to the respective eddy currents to output absolute position signals. For the plate abatement features, the characteristic that may be varied may be a recess depth, an amount of a non-conductive area, an amount of a recessed area, etc. As a varying depth example, the scale may be formed from a bulk material (e.g., aluminum) in which progressively deeper recessed depths are cut along the scale. For plate features, the characteristic that may be varied may include a plate height, an amount of a plate area, etc.