Angular Encoder Index Correction for 3D Measurement Stability
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Solution Overview
Problem
Existing 3D coordinate measurement devices face challenges in maintaining the stability of the absolute angular position of the index mark over time, particularly due to mechanical shocks and eccentricities in the encoder disk alignment, which can lead to errors in distance and angle measurements.
Innovation Solution
A method is introduced for determining a reference correction value for the angular encoder in a laser scanner, involving the use of two read heads and a processor to calculate difference angles based on incremental mark counts and synchronization signals, and applying an angular correction value to stabilize the absolute index position, even in the presence of encoder eccentricity and mechanical shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an incremental angular encoder is used to measure rotation angles, then the device complexity is reduced and ease of manufacture is improved, but the stability of the absolute angular position of the index mark deteriorates over time due to mechanical shocks and encoder disk alignment eccentricities
Solution Approach 1:
The system performs preliminary action by detecting changes in the absolute angular position of the index mark through comparative measurements taken at different times, and then proactively applies correction values to compensate for these changes before they affect measurement accuracy. This prevents the deterioration of reliability rather than merely responding to errors after they occur.
Solution Approach 2:
The patent replaces the mechanical assumption of stable encoder disk alignment with an optical/electronic compensation system. Instead of relying on perfect mechanical alignment that degrades over time, the system uses light reflections from a reference reflector and electronic processing to detect and correct angular position drift, substituting mechanical precision requirements with computational correction.
2Device complexity
If the absolute angular position of the index mark is allowed to drift over time, then device complexity is reduced, but measurement precision deteriorates due to errors in distance and angle measurements
Solution Approach 1:
The system implements feedback by continuously monitoring the absolute angular position of the index mark through comparative measurements, calculating the drift or change in position, and applying correction values to subsequent measurements. This closed-loop feedback mechanism maintains measurement precision without requiring complex mechanical stabilization systems.
Solution Approach 2:
The encoder system performs self-correction by using its own measurements to detect index mark position drift and automatically applying correction values. The system serves itself by identifying and compensating for its own errors without requiring external calibration or intervention, thereby maintaining measurement precision with minimal additional complexity.
3Device complexity
If mechanical shocks and encoder disk alignment eccentricities are not compensated for, then device complexity remains low, but the reliability of 3D coordinate determination deteriorates
Solution Approach 1:
The patent introduces an intermediary correction mechanism that mediates between the incremental encoder measurements and the final 3D coordinate determination. The correction value, derived from comparing absolute index positions at different times, acts as an intermediary that compensates for mechanical shocks and alignment eccentricities, ensuring reliable coordinate determination without requiring complex mechanical stabilization.
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 method ensures that the absolute index position remains stable over time, reducing measurement errors and maintaining accurate 3D coordinate determination despite mechanical shocks and alignment issues, thereby enhancing the precision and reliability of the laser scanner's measurements.
Implementation Method 1
sending the transmission light beam to the reference reflector, reflecting a portion of the transmission light beam as a reference reflected light into the distance meter
Implementation Method 2
one or more optical detectors that convert the received light into electrical signals
Data Source
AI summary
A 3D measurement device sends a beam of light to a point on an object, receives the reflected light, and determines a distance and two angles to the point, one of the angles measured by an angular encoder, which includes a disk having incremental marks and an index mark. Light from the 3D device is rotated to reflect light from a reference reflector to produce a first synchronization signal. A first difference angle is determined based on counts of the incremental marks and on the first synchronization signal. Light from the 3D device is rotated to reflect light from the reference reflector to produce a second synchronization signal. A second difference angle is determined based on counts of the incremental marks and on the second synchronization signal. The reference correction value of the index mark is determined based on the first and second difference angles.