Encoder Interpolation Filter for Propagation Delay Compensation
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Solution Overview
Problem
Digital encoders used in manufacturing robots face challenges in accurately determining the angle position of rotating objects due to propagation delay in signal processing, leading to inaccurate angle position measurements, especially at high rotation speeds, which can limit the precision in fabricating micro-assemblies.
Innovation Solution
A propagation delay compensation and interpolation filter system that includes low pass filters and differentiators to reduce noise and calculate speed and acceleration, allowing for accurate real-time angle position measurement by compensating for delays in analog and digital signal processing, and interpolating or extrapolating data points to correct for invalid or missing data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signal processing is performed to extract angular position from encoder, then digital output is generated, but propagation delay causes inaccurate angle position measurement
Solution Approach 1:
The patent applies preliminary action by calculating speed and acceleration from the angular position signal before the final position output is needed. By pre-computing these derivatives and using them in the delay compensation calculation, the system anticipates the needed correction values, allowing the final compensated position output to be generated with minimal additional delay despite the multi-step processing required.
Solution Approach 2:
The patent changes parameters by transforming the raw angular position signal into speed and acceleration parameters through differentiation. These transformed parameters are then used in the delay compensation formula to calculate the corrected position. This parameter transformation allows the system to compensate for propagation delay by using the relationship between position, velocity, and acceleration to predict the true current position.
2Reliability
If low pass filters are applied to reduce noise, then signal quality improves, but additional propagation delay is introduced
Solution Approach 1:
The patent merges the noise reduction function and delay compensation function into a single integrated filter circuit. Instead of applying noise reduction filtering and then separately compensating for delay, the system combines both operations so that the filter simultaneously reduces noise and compensates for the propagation delay it introduces. This is achieved by incorporating the delay compensation calculation directly into the filter's output stage, using the filtered position, speed, and acceleration signals together to produce the final compensated output.
3Measurement precision
If feedback loop is used to compensate time delay, then accuracy improves, but system becomes unstable and limited in dynamic range
Solution Approach 1:
The patent inverts the conventional feedback approach by using a feedforward calculation method. Instead of measuring the error and feeding it back to correct the position, the system calculates what the true position should be by adding the computed delay compensation (based on pre-calculated speed and acceleration) directly to the measured position. This inversion from feedback to feedforward eliminates the stability issues inherent in feedback loops while achieving the same delay compensation goal.
Data Source
AI summary
Various embodiments provide a filter for propagation delay compensation and interpolation in encoder digital signal processing. The filter can include a first low pass filter configured to reduce noise of a digital input comprising a measured angular position; a first differentiator configured to receive a filtered digital input and to calculate a speed from a difference in time of the measured angular position and a previous angular position; a second low pass filter configured to reduce noise from the speed; a second differentiator configured to receive a filtered speed and to calculate acceleration using a difference in time of the filtered speed and a previous speed; a third low pass filter configured to reduce noise of the acceleration; and a delay compensator configured to receive the filtered digit input, the filtered speed, and a filtered acceleration, and to calculate a propagation delay compensated digital output.