Development of a 3D-printed Angle Sensor for Feedback in Soft Robotic Applications

This thesis describes the early development of 3D printed resistive length sensors to measure bending movement in the soft endoscope. The sensors are printed using fused deposition modelling (FDM) 3D printer with multi-material printing ability. Conductive and non-conductive thermoplastic polyurethane (TPU) are used as the materials of the sensors. The sensors are embedded inside the soft endoscope module during the fabrication of the module.

Vertical module elongation test is done to characterize the resistance change caused by the elongation of the sensors inside the module. Different elongation between the chambers results in bending movement. The bending and orientation angle of the module is converted from the length of each sensor using constant curvature kinematics. The data calculated from the length sensors are compared to the electro-magnetic tracker to validate the usability of the sensors.

The results show that the approach of using 3D printed resistive length sensors to measure bending movement is not the best approach. The non-linearity of the material and its rate dependant hysteresis are big problems in length sensors. Embedding the sensors, although it helps to utilize unused space inside the module, is affecting the strain perceived by the sensors. The measured strain by the sensors is not only the desired elongation but also strain caused by chambers inflation.

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