Characterization and Multichannel Directional Contact Sensing on a Curved Surface Using Flexible Pressure-Sensor Arrays

Abstract

This study presents an embedded flexible pressure-sensing baseball for multichannel finger–ball contact force-trend analysis. Two customized force-sensing resistor arrays were installed beneath the leather surface to monitor ten contact regions associated with the index and middle fingers. A compact analog front-end converts sensor impedance variations into 0–3 V signals, and an STM32-based acquisition unit produces synchronized 10-channel outputs at 180 Hz. The assessment was conducted in two stages. Stage 1 characterized the sensor and measurement chain through loading-jig verification, 19-point quasi-static calibration over 0.1–1.9 kgf, analog-front-end testing, and channel-wise calibration. Stage 2 evaluated the complete baseball under controlled ball-surface loading to determine whether distinct directional and spatial contact patterns could be reconstructed. The loading jig exhibited a transmission error of less than ±1%, and the analog-front-end outputs differed from the calculated values by less than ±1%. Controlled loading produced distinguishable channel-activation, directional force-redistribution, and sequential contact-transfer patterns across the two finger arrays. The 180-Hz output rate corresponds to a 5.56-ms interval and is suitable for synchronized trend observation; however, it is not claimed to reproduce the complete waveform or absolute peak force of the final 10–20-ms pitching-release event. The proposed system is therefore positioned as an embedded platform for sensor assessment and relative contact-force trend analysis. Untethered integration, dynamic reference calibration, and human pitching trials remain future work.