Though palpation is an important technique for distinguishing a tumor, the palpation during thoracoscopic surgery is difficult because of the lack of tactile sense. In order to compensate the surgeon's tactile sense, we developed a forceps with two MEMS (Micro Electro Mechanical Systems) triaxial tactile sensors. In this study, we proposed a tumor size estimation method focusing on the detected force difference according to the hardness of the grasping area. Then, we evaluated the size of tumor models located in the soft tissue models to prove the feasibility of the estimation method. The diameter of the 5 mm and 10 mm spherical tumor models located in the tissue models were estimated 4.6 mm and 10.7 mm, respectively. This result indicates the possibility that the proposed method enables to estimate the size of a tumor within an organ.
