Miniature Force Sensor Based on Dual-Photointerrupter With High Linearity and Disturbance Compensation

This paper presents a photointerrupter based force sensing mechanism to implement a low-cost, high accuracy, and reliable sensor with a miniaturized design. In previous literature, photointerrupter based force sensors have demonstrated a reasonable performance in a cost-effective manner, but have a narrow range of linear output and are significantly susceptible to external disturbances. This makes it difficult to use these sensors in precision force measurement and feedback control. In this work, we present a nonlinear optical model that utilizes a lambertian distribution for the photointerrupter, which is used for optimizing the design parameters of the sensor. The optimized geometry of the screen and a novel dual-screen arrangement are proposed to increase the linear range of the sensor output. A dual-photointerrupter signal acquisition is introduced to compensate the external disturbances and provides robust sensor output. A prototype of the sensor is fabricated in a miniaturized form factor with the ability to measure forces up to 21 N, having 1.08 % nonlinearity, 0.83% hysteresis, and 99.58 % accuracy. The proposed model and sensing mechanisms are experimentally validated.