Optical Measurement Device for Rotating Machine Tip Clearance
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Solution Overview
Problem
Optical clearance measurement in rotating machines is affected by thermal elongation and centrifugal elongation, leading to errors in measured values due to changes in the light sensor and rotary parts, which impact the accuracy of tip clearance calculations.
Innovation Solution
The implementation of a light sensor with slanted and parallel fiber bundles, along with a computation unit that calculates time differences from waveforms detected by light-receiving elements, allows for the correction of thermal elongation effects and eliminates the need for radius calculations, thereby reducing measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical clearance measurement is performed using traditional light sensors in high-temperature environments, then the measurement process can be completed, but measurement accuracy deteriorates due to thermal elongation of the light sensor and centrifugal elongation of the rotary part
Solution Approach 1:
The measurement system is segmented into two independent functional parts: slanted fiber bundles for measuring clearance and parallel fiber bundles for measuring thermal elongation. This segmentation allows each part to perform its specific function independently, enabling the system to compensate for thermal effects without compromising clearance measurement accuracy.
Solution Approach 2:
The parallel fiber bundles act as an intermediary measurement tool that indirectly measures the thermal elongation of the light sensor. By measuring the apparent movement of the target caused by thermal elongation, the system can compensate for this effect in the clearance calculation without directly measuring the sensor's dimensional changes.
2Temperature
If the light sensor housing is made of stainless steel for structural integrity, then the sensor can withstand high-temperature environments, but thermal elongation occurs causing interval AB to increase and adding errors to measured values
Solution Approach 1:
The system changes the measurement parameter from directly measuring clearance to measuring the apparent movement of the target caused by thermal elongation. By using the parallel fiber bundles to measure this apparent movement and then compensating for it in the calculation, the system maintains measurement accuracy despite thermal elongation of the stainless steel housing.
3Measurement precision
If the radius R of the rotary part is used for calculation, then the clearance can be determined, but errors are introduced due to thermal elongation or centrifugal elongation of the rotary part
Solution Approach 1:
The system replaces the mechanical measurement approach (using physical radius R) with an optical measurement approach. By using optical paths and time difference measurements, the system eliminates the need to directly measure or calculate the radius, thereby avoiding errors introduced by thermal and centrifugal elongation of the rotary part.
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 effectively eliminates errors caused by thermal and centrifugal elongation, providing more accurate clearance measurements by calculating the interval affected by thermal elongation and using peripheral speed instead of radius, thus improving the precision of tip clearance determination.
Implementation Method 1
When the rotating blade 71 passes by position C, the light-receiving fibers 61b in the optical fiber bundle 61 receive light reflected from the blade 71 at time t1
Implementation Method 2
a light sensor 60 using optical fibers as illustrated in FIG. 5A is used. This light sensor 60 has a pair of optical fiber bundles 61 and 62
Data Source
AI summary
There is provided: a pair of slanted fiber groups; a pair of parallel fiber groups; a light source for emitting two slanted light beams from a pair of slanted light-emitting fibers, and emitting two parallel light beams from a pair of parallel light-emitting fibers; a target provided to the outer peripheral surface of a rotor; a pair of light-receiving elements for detecting the intensity of light received by each of a pair of slanted light-receiving fibers; a pair of light-receiving elements for detecting the intensity of light received by each of a pair of parallel light-receiving fibers; and a computation unit for performing a computation that includes an interval affected by thermal elongation on the basis of four waveforms indicating changes in the intensity detected by each of the light-receiving elements.