Eddy Current Probe for Turbojet Disc Cavity Inspection
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Solution Overview
Problem
The complex shape of turbojet disc tangential cells makes conventional eddy current testing difficult, expensive, and requires specific probes for each type of cell, with challenges in applying the probe without damage, maintaining constant speed during scanning, and detecting faults regardless of their orientation.
Innovation Solution
A non-destructive testing device with a probe body featuring an eddy current sensor and a rod with a resilient biasing mechanism, where the sensor is installed laterally and embedded in a curved boss, allowing for almost point contact and stable scanning along rectilinear strokes, and a robot for precise movement and orientation to explore the entire surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a specific probe is developed for each type of cell to match the complex shape, then the detection reliability is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies universality by designing a single probe body with a universal curved boss that can accommodate multiple sensor types and configurations. The probe body serves multiple functions: it provides a universal mounting structure for different sensors, maintains consistent contact geometry through the curved boss, and enables inspection of various cell types without requiring probe redesign. This resolves the contradiction by achieving detection reliability through standardized geometry while reducing device complexity by eliminating the need for multiple specific probes.
Solution Approach 2:
The patent applies parameter changes by varying the sensor type, orientation, and positioning within the same probe body structure. The curved boss geometry remains constant, but parameters such as sensor coil orientation (azimuthal angle), sensor type (eddy current, acoustic emission, etc.), and sensor positioning can be changed to detect different defect orientations. This allows a single probe design to reliably detect defects in various orientations and cell types without increasing overall probe complexity.
2Reliability
If the probe is applied with impact to ensure contact, then the contact reliability is improved, but the sensor may be damaged
Solution Approach 1:
The patent applies beforehand cushioning by using the resilient biasing means (springs) to provide continuous contact force between the curved boss and the cavity surface. This elastic element cushions the contact, preventing impact forces from reaching the sensor while maintaining reliable contact pressure. The spring acts as a shock absorber that protects the sensor from damage during probe insertion and movement, while ensuring consistent contact for reliable sensing.
Solution Approach 2:
The patent applies the principle of flexible elements through the use of resilient biasing means (springs) that provide flexible contact pressure. The elastic spring allows the probe body to adapt to surface variations while maintaining contact, and absorbs impact forces that would otherwise damage the sensor. This flexible contact mechanism ensures reliable sensing without compromising sensor durability.
3Measurement precision
If the sweeping is done at constant speed over the entire length, then the measurement consistency is improved, but the productivity decreases due to time constraints
Solution Approach 1:
The patent applies self-service by using the resilient biasing means to automatically maintain constant contact pressure between the curved boss and the cavity surface during scanning. The spring automatically compensates for variations in contact conditions, ensuring consistent measurement pressure without requiring external control. This self-regulating contact mechanism maintains measurement consistency while allowing the probe to be moved at optimized speeds for productivity.
Solution Approach 2:
The patent applies dynamics by allowing the probe system to adapt its contact pressure dynamically through the resilient biasing means. The spring automatically adjusts the contact force based on the local geometry and surface conditions, maintaining optimal contact pressure throughout the scanning process. This dynamic contact maintenance ensures measurement consistency while enabling flexible scanning speeds for improved productivity.
4Strength
If the sensor is positioned away from the cavity wall to avoid interference, then the sensor protection is improved, but the detection capability decreases
Solution Approach 1:
The patent applies the intermediary principle by using the curved boss as a mediator between the sensor and the cavity surface. The boss provides a protective interface that maintains a safe distance between the sensor and the cavity wall, preventing direct contact and potential damage. At the same time, the curved geometry of the boss ensures optimal positioning of the sensor relative to the generatrix being scanned, maintaining detection capability through proper geometric relationship rather than direct contact.
5Productivity
If vibrations are allowed during scanning, then the scanning speed can be increased, but the measurement reliability deteriorates
Solution Approach 1:
The patent applies beforehand cushioning by using the resilient biasing means to dampen vibrations before they can affect the sensor measurements. The spring element acts as a vibration isolator, absorbing high-frequency vibrations generated during scanning while maintaining steady contact pressure. This vibration cushioning allows for higher scanning speeds without compromising measurement reliability, as the resilient element filters out detrimental vibrations.
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 solution enables reliable detection of defects in turbojet disc cells without damaging the surface, reduces vibrations, and improves measurement reliability by ensuring consistent contact and precise scanning, allowing for efficient and automatable testing of complex cavities.
Implementation Method 1
Device for inspecting a rectilinear cavity using Foucault currents
Implementation Method 2
sensor (24) consisting of one or two coils supplied with high frequency currents
Data Source
Figure 1~4
Figure 5
AI summary
Control of an open cavity by successive pinning of an eddy current sensor. The control device comprises a probe body (20) including the sensor (24) installed laterally near the end of a rod (22) and in the extension of a ramp (30) and elastic loading means acting on the probe body.