Development of a three-dimensional tactile sensor for minimally invasive instruments

Abstract

This paper proposes a three-dimensional tactile sensor that can be attached to the tip of an endoscope or catheter to detect the tip contact conditions. Because conventional minimally invasive instruments (MIIs) without a sensor cannot detect the posture and applied force at the tip, operators cannot obtain accurate information during minimally invasive surgery (MIS). The sensor consists of an elastic cylinder and three strain g auges. The gauges, located on the surface of the cylinder at intervals of 120 � , are used to detect deformation of the cylinder caused by contact with the inner walls of the patient's organs. The output voltage signals of the gauges are approximated by a sinusoidal function with a phase difference of 120 � . The three-dimensional contact angle and applied force at the tip of the sensor can be estimated accurately from the three sinusoidal functions and measured output voltage signal from the gauges. The operating principle of the sensor is examined through several experimental conditions. To improve the effectiveness of minimally invasive surgery (MIS), it is necessary to develop better endoscope and catheter techniques. Conventional minimally invasive instruments (MIIs) improve the quality of life (QOL) of patients, because they can begin rehabilitation only a few days after MIS. However, the manipulation of MIIs is difficult because opera tors cannot obtain accurate information about the tip contact conditions of MIIs with the walls of the patient's organs. In conventional MIS, the operator manipulates the MII based on both the tactile sensations transmitted to their hand via the MII and the two-dimensional X-ray image information. However, tactile sensations are a mixture of the contact and friction forces with the walls of organs, and it is difficult to discriminate these forces precisely. Therefore, operators need to be highly trained; a lack of this skill on their part may lead to critical accidents. The abovementioned issues have necessitated the development of mechanisms for detecting the posture of the MII tip. Some active devices (1-4) have been developed to help manipulate catheters (3) and endoscopes (4). In these devices, shape memory alloys (SMAs) are used as actuators. In addition, inchworm locomotion (5) has been developed. An inchworm-like robot with a bellows mechanism