Opto-Mechatronic–Electrical Synergistic Capacitive Sensor for High-Resolution Micro-Displacement Measurement Targeting Cost-Sensitive Applications

To address the limitations of optical interferometry (strict environmental requirements, high cost) and piezoelectric methods (hysteresis, creep) in micro-displacement measurement, this study proposes a collaborative measurement approach based on the parallel plate capacitance principle—with its core innovation lying in integrated optimization rather than original principles. Unlike existing studies that separately optimize mechanics, hardware, or algorithms, this work achieves the first synergy of three components: a mechanical coupling mechanism (integrating a high-resolution optical mount and a micrometer) for parallel plate regulation, a 21-bit capacitance detection module based on the STM32-PCAP01 (with a resolution of 0.0001 pF), and a linear response model relating capacitance to the reciprocal of displacement. Experimental validation confirms its engineering feasibility for sub-nanometer-level precision: with a 10 cm plate radius and 3–20 mm initial spacing, the system achieves 277.215 ± 0.244 pF·mm sensitivity and <0.05 μm displacement resolution. The relative error of micro-displacement measurement in the 10 μm range is less than 1.56%. Based on the hardware resolution, the system possesses the theoretical capability to detect displacements as low as 10−8 to 10−9 m. Compared to laser interferometry, it operates stably in common industrial environments without vibration isolation or darkrooms, reducing costs by ~90% while maintaining comparable accuracy. This cost-effective solution enables online precision measurement in semiconductor manufacturing and MEMS testing, with its multi-physics collaborative design offering a new paradigm for intelligent sensor development.