Freeform measurement method based on differential confocal and real-time comparison

Area of Science:

• Metrology
• Optical Engineering
• Manufacturing Science

Background:

• Accurate measurement of freeform surfaces is critical in advanced manufacturing.
• Existing methods struggle with surfaces exhibiting large roughness and local inclination.
• Contactless measurement is preferred to avoid surface damage and ensure precision.

Purpose of the Study:

• To develop a high-precision contactless measurement method for freeform surfaces.
• To address the challenges of measuring surfaces with large roughness and local inclination.
• To reduce spatial motion errors during measurement.

Main Methods:

• Utilizing a laser differential confocal trigger sensor (LDCTS) for surface profile acquisition.
• Implementing a real-time comparison method using reference planes (RCMRP) to correct for errors.
• Employing an error model to separate straightness and rotation errors.
• Integrating LDCTS with RCMMRP for enhanced measurement capabilities.

Main Results:

• Achieved an inclination measurement capacity exceeding 25 degrees.
• Improved repeated measurement accuracy to better than 10 nm over a 150 mm x 150 mm scanning range.
• Demonstrated a five-fold improvement in repeated measurement accuracy compared to non-RCMRP methods.
• Successfully reduced dominant straightness and rotation errors, minimizing spatial motion errors.

Conclusions:

• The combined LDCTS and RCMMRP method offers a robust strategy for high-precision freeform surface measurement.
• The technique is effective for surfaces with significant local inclination and roughness.
• This method enhances measurement accuracy and reliability during various manufacturing stages.