A Miniaturized Triaxial Force Sensor with Independent Axial and Transverse Force Sensing

Unmet Need
Lack of force sensing is one of the most formidable technical challenges in retinal microsurgery. Incorporating high sensitivity force sensing into the ophthalmic tools has thepotential to provide the surgeon useful force feedback and to enable safe robotic assistance.  Forces exerted in retinal microsurgery are generally well below the human sensory threshold.  75% of forces applied during in vitro retinal manipulation in porcine cadaver eyes are less than 7.5 mN, and only 19% of the events at this force level can be felt by the surgeons.  Large forces are undesired and can potentially damage the delicate retina. Incorporating force sensing capability into the ophthalmic instrument enables quantitative monitoring of force applied during retinal mircosurgery. It can be used to provide awareness of subtactile tool-tissue forces to the surgeon. The technology can also be incorporated into robotic systems to provide haptic feedback and motion guidance.
Technology Overview
A miniature force sensor is integrated into a small interventional tool that can measure 3-dimensional (3D) forces. The force sensor has a diameter of 0.9 mm and a length of 8 mm. Its size can be further reduced to 0.63 mm in diameter and 3-5 mm in length. It enables triaxial force sensing with very fine sensitivity. The force sensing resolution is less than 1 mN in axial direction and less than 0.2 mN in transverse direction.  The force sensor uses a flexure to decouple axial and transverse force sensing and to improve the axial force sensing sensitivity with the flexure elasticity. At the same time, the flexure minimizes the axial force sensing noise attributed to transverse forces.   In addition, miniature strain sensors are configured to decouple axial and transverse force sensing and to improve the independent force sensing performances in axial and transverse directions. 
Stage of Development: 
Fiber optic strain sensors are used in the proof of concept prototype, while other strain sensors can be adopted too, such as strain gauges, piezoelectric sensors, and other optical strain sensors, etc. 


Publications: 
Proc. IEEE RAS & EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob) August 12-15, 2014. São Paulo, Brazil.
 

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