Dual-Encoder Interpolation Error Reduction via Spatial Filtering
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Solution Overview
Problem
Position encoding devices, particularly incremental encoders, suffer from significant interpolation error due to factors like imbalance in output signal amplitudes, scale pitch periodicity errors, non-zero bias signals, and manufacturing irregularities, which compromise their accuracy and precision.
Innovation Solution
A dual-encoder system with a signal processing unit is employed, where two encoders with different scale pitches are offset from each other. This system generates pairs of position measurements in the time domain, which are then converted into the spatial domain to create a map of differences, identifying and filtering interpolation error patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single encoder with a given scale pitch is used, then the device complexity is low, but the measurement precision is limited by interpolation error
Solution Approach 1:
The system divides the measurement task into two independent encoder channels, each with different scale pitches. By segmenting the measurement function across multiple encoders with distinct pitch characteristics, the system captures multiple spatial frequencies of the same position, enabling error identification and elimination through comparison.
Solution Approach 2:
The invention changes the scale pitch parameter between the two encoders to create different spatial sampling patterns. This parameter variation allows the system to observe the same physical position through different spatial frequencies, making interpolation errors distinguishable and removable through signal processing.
2Measurement precision
If a single encoder is used, then the device complexity is low, but the ability to identify and eliminate interpolation error is insufficient
Solution Approach 1:
The system uses feedback by comparing measurements from two encoders with different scale pitches. The signal processing unit continuously analyzes the difference between measurements, identifies periodic error patterns, and eliminates them to produce corrected position data, creating a closed-loop error compensation mechanism.
Solution Approach 2:
The invention introduces asymmetry by using encoders with different scale pitches rather than identical configurations. This asymmetric setup creates distinct measurement signatures that allow the system to differentiate between true position changes and interpolation errors, enabling error identification and removal.
3Measurement precision
If two encoders with different scale pitches are used, then the measurement precision improves through error identification, but the device complexity increases
Solution Approach 1:
The measurement function is segmented into two independent encoder channels with different scale pitches, allowing parallel measurement of the same position. This segmentation enables the system to capture multiple spatial frequencies and identify interpolation errors through comparison.
Solution Approach 2:
The scale pitch parameter is varied between the two encoders to create different spatial sampling characteristics. This parameter change allows the system to observe the same physical position through different spatial frequencies, making interpolation errors distinguishable and removable.
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 proposed solution effectively reduces interpolation error by identifying and eliminating periodic and non-periodic error patterns, thereby enhancing the overall accuracy and precision of position measurements, even with relatively inexpensive encoders.
Implementation Method 1
An optical encoder is one well-known type of position encoder that relies upon the principles of interference, reflectance, or transmission of light in order to measure movement
Implementation Method 2
An optical encoder is one well-known type of position encoder that relies upon the principles of interference, reflectance, or transmission of light in order to measure movement
Implementation Method 3
Light reflected from the track is directed onto a photodetector in the optical encoder. As the scale moves in relation to the encoder head, photodetector output signal changes
Data Source
AI summary
A system for measuring movement along a designated travel path includes an encoder assembly with a pair of encoder heads maintained a fixed distance apart. The encoder assembly is designed to simultaneously compile pairs of position measurements relative to a main track, with each encoder head utilizing a unique scale pitch. A signal processing unit in communication with the encoder assembly converts each pair of position measurements into the spatial domain and maps the calculated distance between position measurements. The signal processing unit identifies patterns in the mapped data which are directly attributable to interpolation error, for example, by performing either a fast Fourier transform or a discrete Fourier transform on the mapped data to yield spatial frequency peaks. Thereafter, the signal processing unit can filter out mapped data at the peak frequencies to minimize errors that may otherwise compromise encoder measurement accuracy.