Endoscopic palpation is a developing technology that shows promise in identifying early stage small tumors located beneath the surface of an organ. This technology requires sensors to detect the stiffness difference between stiff tumors and soft healthy tissue. This paper proposes a three-axis ballpoint-pen-type force sensor that can scan the surface to measure both shear and reactive forces, which can be used to calculate the distribution of stiffness. The sensor design includes five capacitors, four of which are formed at the lateral side of the cylindrical silicone rubber body. Fabrication of the electrodes is achieved by filling the pockets of a molded polydimethylsiloxane structure with liquid metal. The manufactured sensor was capable of identifying the magnitude and orientation of an applied shear force at 1 N. Detection of a stiff region was also successfully demonstrated.
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