Quartz pendulum reeds are essential components in high-precision quartz flexural accelerometers. These accelerometers are widely used in aerospace, aviation, navigation, and even in civil applications like seismic monitoring and oil drilling. To ensure their performance, especially in navigation systems, it is crucial to measure the thickness of these quartz reeds with high accuracy.
Traditional contact-based thickness measurement methods—such as micrometers or inductive sensors—can easily damage the fragile reeds, are time-consuming, and provide inconsistent results. To solve these problems, researchers proposed a non-contact measurement method using a chromatic confocal sensor to achieve faster, safer, and more accurate results.
Why Quartz Reeds Need Precise Measurement
Quartz pendulum reeds play a critical role in sensing acceleration in various advanced instruments. The thickness of the reed directly impacts the sensitivity and accuracy of the accelerometer. However, current manual contact-based methods:
Have low precision
Risk damaging the part
Are slow and labor-intensive
Result in lower production yield
To overcome these challenges, a non-contact optical method using a chromatic confocal sensor was introduced.
How Chromatic Confocal Sensors Work
Chromatic confocal sensors use white light as a source and can focus different wavelengths at different distances. Here’s how the system works:
Light is split into different wavelengths and focused on the surface of a transparent object.
Each wavelength corresponds to a specific position in space.
When the light reflects from the surface of the object, the system detects the wavelength of the reflected light to calculate the exact position.
For transparent objects like quartz reeds, the system captures two reflections—one from the top surface and one from the bottom.
The distance between these two reflections gives the thickness of the object.
This technique allows high-precision, non-contact measurements—even for transparent or layered materials like glass and quartz.
Measurement Setup
In the measurement system:
The quartz reed is fixed on a stable platform.
The chromatic confocal sensor is positioned directly above the reed, perpendicular to its surface.
The sensor captures reflected signals from both the top and bottom surfaces.
The system calculates the distance between the two surfaces to determine thickness.
This setup eliminates physical contact and minimizes the risk of damaging the sample.
Measurement Uncertainty Analysis
To ensure reliable measurements, the team analyzed possible uncertainties:
Sensor Accuracy
Resolution: 50 nm
Accuracy: ±300 nm
Resulting uncertainty: ±0.17 μm
Positioning Error (Reed Tilt)
Caused by slight tilting during placement
Maximum tilt: 1.3°
Resulting uncertainty: ±0.12 μm
Material Properties
Variations in refractive index and surface roughness
Estimated uncertainty from refractive index: ±0.8 μm
Estimated uncertainty from surface roughness: ±0.8 μm
Total combined uncertainty:
Using root-sum-square method:
→ ±1.15 μm
Results and Conclusion
The non-contact measurement system was tested and proved to be:
Accurate
Repeatable
Efficient
Damage-free
The results clearly show that this method is superior to traditional manual approaches, especially for high-precision applications in aerospace and defense.
Conclusion:
Using chromatic confocal sensors for quartz reed thickness measurement greatly improves measurement precision and reliability. It eliminates contact-based risks, reduces labor intensity, and supports the production of high-performance navigation components.
