Flexible, highly articulated robotic tools can greatly facilitate procedures in which the operator needs to access small openings and confined spaces. Particularly, in the context of robotic-assisted minimally invasive surgery (RMIS), the application of such manipulation tools can be significantly beneficial in preventing unnecessary interactions with sensitive body organs by which reducing patient’s recovery time when compared with conventional methods. However, these systems usually lack tactile feedback and are not able to perceive and quantify the interactions between themselves and soft body organs. This deficiency may result in damaging the organs due to unwanted excessive force applied. To this end, we introduce a contact force sensor based on three 'dyadic-S-shaped' beams and three optoelectronic sensors. The modular design of a flexible manipulation system described as part of this paper allows ready integration of a series of the proposed sensors within its structure. The sensor uses our novel sensing principle for measuring contact forces. The strategic employment of custom sensor structure and the optoelectronic components fulfill our design objectives which has been focused on the creation of a modular, low-cost, low-noise (electrically) with large voltage variation, without the need for an amplifier, through a simple fabrication process for MIS. Our experimental results, following a very simple calibration processes show the average errors of Fx (+19.37%±0.82, -18.32%±2.06) and Fy (+18.56%±1.69, -17.00%±1.32), and the average RMS errors of Fx (0.12N±0.0067) and Fy (0.11N±0.0032) in the measurement of force values within
the range of -4 to 4 N.

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