Development of a High-Precision Optical Force Sensor With μN-Level Resolution

Abstract

Unknown micro-contact forces may affect operation accuracy in micro-operation technology and high-precision contact measurement. Existing micro force sensors are unable to meet the demand for high resolution, large range, and low cost. Therefore, a more economical solution for high-precision force measurement is needed. A high-precision optical force sensor (OPFS) with a simple sensing principle is proposed in this study. The OPFS is mainly composed of a laser diode, a force-sensitive structure, and a four-quadrant photodetector (QPD). When force is applied to the measuring platform, the force-sensitive structure produces the corresponding elastic deformation, which is sensed by the QPD. The multi-range and customized resolution of the OPFS can be achieved by adjusting the stiffness of the force-sensitive structure. The design and optimization of the OPFS are completed via theoretical modeling and simulation analysis. The performance of the OPFS is examined experimentally. The OPFS is found to have a sensitivity of 0.27 mV/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{N}$ </tex-math></inline-formula> , a measuring range of 0–2.71 mN, and a resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$32\mu \text{N}$ </tex-math></inline-formula> . The measurement uncertainty of the OPFS due to nonlinearity, resolution, repeatability, and drift is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$82\mu \text{N}$ </tex-math></inline-formula> . The effectiveness of the OPFS in the measurement of micro-forces is verified. Finally, the OPFS is used to measure the contact force of a micro/nano contact probe. The results show that OPFS can be used for force calibration in micro/nano contact measurement instruments.