Low-thermal-drift MEMS 3D Force-sensing Chip Integrated with a Surgical Gripper for Endoscopic Continuum Robots

Endoscopic continuum robots hold great promise for minimally invasive surgery in natural orifices, but the confined space at the distal end of surgical instruments makes it difficult to obtain accurate three-dimensional (3D) operative force information. To address this challenge, a low-thermal-drift micro-electro-mechanical systems (MEMS) 3D force-sensing chip that can be integrally embedded in the distal gripper is developed. The chip exploits the differential strain distribution of a central membrane under normal and tangential loads, and uses the differential outputs of four high-strain piezoresistive sensing units to achieve decoupled measurement of distal 3D operative forces; by integrating four on-chip wheatstone piezoresistive full bridges that share a uniform thermal field on the same silicon die, temperature-induced common-mode drift is cancelled and sensitivity variation with temperature is suppressed. The force-sensing chip is fabricated using a MEMS micromachining process, with a compact size of only 2mm × 2mm × 0.4mm, and is assembled via a rigid-flex hybrid packaging scheme to enable integral embedding into the distal surgical gripper of an endoscopic continuum robot. Experimental results show that the tri-axial outputs exhibit good linearity (R²=0. 999) over the 0~4 N range; the normalized zero-offset drift over 25~85℃ is about one seventh that of a conventional quarter-bridge chip, and the sensitivity remains nearly constant between 25~50℃, confirming the stability and reliability of the proposed chip for force sensing in endoscopic minimally invasive surgery.