In laparoscopic surgery large instruments cannot be used because they cannot pass through trocars which are typically smaller than 12mm in diameter. For example, retracting an internal organ with a slender instrument is often a difficult task. To remove this limitation, we have proposed “assemblable instruments”, that is, parts are inserted through trocars and assembled inside the abdominal cavity to become a large instrument and we have developed assemblable hands. However they use two trocars for assembling, which require positioning and alignment of two assembled parts. This paper presents a simple three fingered hand whose function is limited to retracting. We propose a much simpler assembling method “single trocar assembling” for the hand. Experimental results verify that the hand can be assembled easily and that it can withstand a force of 25N enough to rectract a pancreas.

In laparoscopic surgery, surgeons perform surgery in the abdominal cavity by using only slender instruments that can be inserted through small diameter trocars. When it is difficult to perform surgery by using only instruments for laparoscopic surgery, they often make a 7–8 cm incision through which their hand can be inserted. Clearly this is invasive compared with complete laparoscopic surgery. This paper proposes an assemblable mechanical hand like a human hand that can be inserted through trocars. We already developed a three-fingered three-degree of freedom assemblable hand. The purpose of this paper is to develop an assemblable hand with more degrees of freedom that can grasp/push aside large internal organs and open membranes. The developed hand has three fingers with a total of five degrees of freedom. Its power transmission mechanisms and assembling method are completely different from those of the previous hand. The hand is assembled from body and finger units with an installation tool. The finger unit is fixed to the body unit with only one screw by using the installation tool. To drive the fingers, power is transmitted with cables, gears and shafts. Experimental results verify that the hand can be assembled in a closed space and that it can grasp and push aside various objects.