Automatic Stop System for Avoiding Over Cut in Implant Surgery Using Haptic Drilling Robot
Statements of the problem
In dental implant surgery, surgeons are required advanced techniques and extensive experiences to correctly handle the cutting device. The lack of techniques and experiences may bring on an over cut and damages to the surrounding tissue. As a result, this situation has risks of causing the subsequent complications or life-threatening accidents by heavy bleeding and nerve damage during surgery. The supporting technology for the surgeon is required to prevent these accidents. In order to solve this problem, we developed a haptic drilling robot [1]. In this research, an automatic stop system for the haptic drilling robot will be proposed.
Materials and methods
The system consists of a master robot and a slave robot. The master robot is a robot that surgeons operate, and the slave robot is a robot that interacts with the cutting material. The force and position of the master robot and the slave robot are transmitted in both directions by bilateral control. The proposed method can be divided in two parts. The first part is the cutting depth estimation by the contact detection based on a frequency analysis of the thrust force vibration [2]. The second part is the position limitation by implementing the force scaling function. First, the cutting depth can be obtained in the real-time by the contact detection from the threshold calculated by the frequency analysis and the thrust force vibration model. When the drill reaches the position limitation, it automatically stop by the force scaling function because a large scaling will decrease the force that transmitted to the slave robot. Therefor, the slave robot can not apply enough cutting force to cut the material.
Results
A pine wood with the thickness of 5 mm was used as a phantom, which was mentioned in Misch’s bone density classification. It has same hardness of porous cortical bone and dense trabecular bone. Values in the force scaling function were calculated from the relation of the maximum motor torque and the cutting force of the phantom. Experiments were conducted for ten times. From the experimental results, although the force of master robot was increased, the force scaling function decreased the force of slave robot. It made slave robot stopped around the position limitation and the error was in 60 μm. It is only 2.5 % of 2 mm margin; which is necessary to have between implant and landmarks.
Conclusions
The purpose of this research is to achieve automatic stop system. The validity of the proposal was confirmed through experiments using a phantom mentioned in Misch’s bone density classification. From these experimental results, the drill could successfully stop within 60μm from the position limitation. Higher accuracy was expected by fine adjustment in force scaling.
References
[1] Y. Kasahara, H, Kawana, S. Usuda, and K. Ohnishi, “Telerobotic-assisted bone-drilling system using bilateral control with thrust operation scaling and cutting force scaling.”, International Journal of Medical Robotics, vol. 8, no. 2, pp. 221-229, June 2012.
[2] K.Yu, S. Iwata, K. Ohnishi, S. Usuda, T. Nakagawa, and H. Kawana, “Modeling and Experimentation of Bone Drilling Vibration for Cutting Force Presenting System,”. Proceeding of The 13th International Workshop on Advanced Motion Control, Yokohama, Japan, March 16th, 2014.