Optical Sensor for Scanning Angle of Micromirror with Improved 2D Calibration Method

The optical angle sensor demonstrates considerable potential to supersede the piezoresistive sensor as the preferred angle detection mechanism for micromirrors, primarily due to its reduced vulnerability to temperature fluctuations. However, this sensor is susceptible to interference from rotations about non-detectable axes and exhibits inadequate linearity. To mitigate these challenges, this paper introduces a sub-region calibration method. A mapping surface was created to link the output signal offsets of two axes with their input angles, allowing the effects of non-measured axes to be treated as variables. To simplify the mathematical model of this mapping surface, it was divided into an n-by-n grid of small areas. Each area uses bilinear interpolation to calculate the corresponding angle from the output values. To quickly locate which grid area a sensor output belongs to, the entire mapping surface was scaled to a range from 0 to n. Sensor outputs are then assigned to specific grid areas using the floor function. For validation, an optical sensor and a 2D rotating stage were built for calibration tests. Experimental results show that this calibration method keeps measurement errors below 0.01° within a ±8° operating range of the sensor.