Absolute Distance Meter Drift Reduction via Optical Switching
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Solution Overview
Problem
Absolute distance meters (ADMs) face significant drift issues due to variations in optical and electrical components, particularly in monostatic laser trackers used for high-accuracy industrial measurements, which affect the accuracy of distance measurements, especially when measuring moving targets.
Innovation Solution
The implementation of a fiber switching network with at least one optical switch that alternates between measure and reference modes, utilizing a single channel detector and signal processor to minimize drift by multiplexing optical signals and processing them in a temporally spaced manner, thereby reducing common mode errors in both optical and electrical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate optical and electrical channels are used for measure and reference paths, then the system can process signals independently, but drift errors accumulate due to component variations
Solution Approach 1:
The patent merges the optical switching function and electrical signal processing into a single integrated optical switch that handles both measure and reference channels. This consolidation ensures that both channels experience identical environmental conditions and component variations, causing drift errors to become common-mode signals that can be subtracted out during processing, thereby improving measurement precision while maintaining reliability
Solution Approach 2:
The patent introduces a common optical switch as an intermediary component that both measure and reference channels pass through. This intermediary ensures that environmental variations affect both channels equally, allowing the system to use differential measurement techniques to eliminate drift errors and achieve higher measurement accuracy
2Productivity
If multiple separate detectors are used for measure and reference channels, then signal processing can be parallelized, but device complexity and drift errors increase
Solution Approach 1:
The patent combines multiple detector functions into a single detector that sequentially receives signals from both measure and reference channels through the optical switch. This reduces the total number of optical components and simplifies the device structure while maintaining processing capability through temporal multiplexing, where the single detector alternates between measuring reference and measure signals in rapid succession
Solution Approach 2:
The patent implements periodic switching between reference and measure channel detection using the optical switch. The single detector operates in periodic cycles, alternating between receiving reference signals and measure signals. This periodic action maintains productivity by ensuring both channels are processed regularly while reducing device complexity by eliminating the need for multiple simultaneous detectors
3Measurement precision
If optical switches are used to multiplex channels, then drift is reduced through common mode error cancellation, but insertion loss increases
Solution Approach 1:
The patent uses the optical switch to create temporal copies of the detection function for both measure and reference channels. Instead of requiring separate physical detection paths that would each incur independent losses, the single detector sequentially copies its detection capability to handle both channels through time-division multiplexing. This approach reduces drift by ensuring identical detection conditions while managing insertion loss through efficient switching design
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 approach significantly reduces drift in ADM systems, enabling more accurate and stable distance measurements for both stationary and moving targets, improving the overall precision and reliability of the laser tracker's distance measurement capabilities.
Implementation Method 1
a fiber switching network having at least one optical switch that switches between at least two positions in response to a switch control signal
Implementation Method 2
a single channel detector that detects the measure and reference light beams in a temporally spaced multiplexed manner and provides an electrical signal
Data Source
AI summary
An absolute distance meter (ADM) that determines a distance to a target includes a light source that emits an emitted light beam. The ADM also includes a fiber switching network having at least one optical switch that switches between at least two positions in response to a switch control signal, a first one of the positions enabling a measure mode in which the emitted light beam is emitted from the fiber switching network towards the target and is reflected back as a measure light beam into the fiber switching network, a second one of the positions enabling a reference mode in which the light beam comprises a reference light beam within the fiber switching network. The ADM further includes a single channel detector that detects the measure and reference light beams in a temporally spaced multiplexed manner and provides an electrical signal which corresponds to the detected measure and reflected light beams. Also, the ADM includes a single channel signal processor that processes the electrical signal and provides a conditioned electrical signal in response thereto, and a data processor that processes the conditioned electrical signal to determine the distance to the target.