Inductive Encoder Shield Structures Against Stray Field Offsets
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Solution Overview
Problem
Inductive encoders face challenges in achieving a combination of high accuracy, high resolution, robustness to contamination, compact size, and low cost, with stray magnetic fields inducing errors in position calculations due to parasitic sensor loops.
Innovation Solution
The implementation of shield structures comprising shield vias and shield loops that partially shield sensor vias from stray magnetic fields, reducing the formation of parasitic sensor loops and associated offset signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensor vias are used to connect sensing elements to external circuits, then electrical connectivity is achieved, but stray magnetic fields couple to parasitic loops formed by the vias causing offset signals and measurement errors
Solution Approach 1:
A shield structure comprising shield vias and conductor portions is introduced as an intermediary element between the sensor vias and the stray magnetic fields. The shield vias are coupled by conductor portions to form shield loops that act as a barrier, preventing stray magnetic fields from coupling directly to the parasitic loops formed by sensor vias, thereby eliminating offset signals while maintaining electrical connectivity.
Solution Approach 2:
The shield structure converts the potentially harmful effect of stray magnetic field coupling into a beneficial shielding effect. By intentionally creating controlled conductive paths through the shield vias and conductor portions, the design harnesses electromagnetic induction principles to generate opposing magnetic fields that cancel out the harmful stray fields, protecting the sensor vias from interference.
2Ease of manufacture
If the encoder design is simplified for low cost and ease of manufacture, then manufacturing complexity is reduced, but achieving high accuracy and resolution becomes more difficult
Solution Approach 1:
The invention changes the structural parameters of the encoder by integrating shield vias and conductor portions directly into the PCB layers. This parameter change allows the shield structure to be formed using standard PCB fabrication processes, maintaining ease of manufacture while significantly improving measurement precision by eliminating offset signals caused by stray magnetic field coupling.
Solution Approach 2:
The shield structure is merged with the existing PCB structure by forming shield vias and conductor portions within the same PCB layers. This integration combines the shielding function with the structural support and electrical connectivity functions of the PCB, achieving high measurement accuracy without adding separate complex shielding components, thus maintaining manufacturing simplicity.
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
Enhances the accuracy and reliability of inductive encoders by minimizing signal offsets caused by stray magnetic fields, thereby improving position measurement precision.
Implementation Method 1
a field generating portion PRTFGE configured to generate a changing magnetic flux in response to a drive signal; and a sensing portion PRTSEN configured to provide detector signals which respond to a local effect on the changing magnetic flux
Implementation Method 2
The plurality of shield structures SST are configured to at least partially shield the set of sensor vias from stray magnetic fields that result from the operation of the field generating portion PRTFGE
Data Source
AI summary
An inductive encoder system includes a scale including a periodic scale pattern, and a detector portion configured to move along a measuring axis direction relative to the periodic scale pattern. The detector portion includes a field generating portion configured to generate a changing magnetic flux, and a sensing portion comprising one or more sets of sensing elements and configured to provide detector signals which respond to a local effect on the changing magnetic flux provided by the periodic scale pattern, wherein each set of sensing elements is coupled to a set of sensor vias. The detector portion further includes a plurality of shield structures SST, wherein each shield structure SST is located proximate to a set of sensor vias and comprises a plurality of shield vias, and in each shield structure one or more shield loops are formed by the plurality of shield vias as coupled together by conductor portions.