Small Medical Robot

Introduction

An endoscope is a flexible tube used to examine the interior of the human gastrointestinal tract; it is inserted via the mouth or anus and manually pushed into the organ to be examined. In contrast, a capsule endoscope (Figure 1) is swallowed by a patient and naturally exits the body within eight hours (Moglia et al., 2009).

Figure 1.

Capsule endoscope “Sayaka,” ©RF SYSTEM lab

Another type of capsule endoscope requires a permanent magnet mounted inside it, and the capsule moves when a rotational magnetic field is applied (Ishiyama a et al., 2001; Chib et al., 2005). M. Shikanai et al. developed a robotic endoscope that consists of front and rear bodies with bidirectional rotational helical fins (Shikanai, 2009). A DC motor connects the front and rear, and clockwise rotation of the front body and anticlockwise rotation of the rear body propel the robot through the intestines. These capsule-type robots require power supply wires and a permanent magnet. A potential problem with this design is that rotational drive could cause engulfment.

Medical doctors and researchers are now working together to develop a novel capsule-type medical robot, the concept of which is shown in Figure 2. The robot remains in the abdominal cavity in order to monitor sites of medical interest, and data is captured through travel, surveillance, manipulation, and communication operations. The project team is responsible for developing three components of the device: the internal computer hardware and software technologies for steering control, micro-sensing and manipulation.

Figure 2.

Concept of a new capsule type medical robot in the abdominal cavity

This chapter focuses on my research, which is the steering control technology for the capsule-type medical robot. Section II discusses actuators suitable for the internal driving mechanism and robot operation and specifications. Section III describes robot movement experiments conducted in a living organism for the purpose of verifying our proposed principle of robot travel. Section IV presents the results of a modified clinical prototype, and Section V discusses the conclusions of this project.

Medical Robot Operation

In discussing actuators suitable for internal robot operation, the first question is whether or not robots should have actuators.

In the case that an internal robot has actuators such as a rotation motor (Rentschler et al., 2007), a shape memory alloy actuator (Haga et al., 2004; Ikuta et al., 1988), a pneumatic actuator (Carrozza et al., 2003) or an impact drive actuator (Ikuta et al., 1994) to initiate travel, the drive motor is powered by electromagnetic induction and the energy is stored in a built-in condenser. In this way the robot can be constantly mobile. However, the motor and transmission require space, and miniaturization is difficult.

In the case that an internal robot does not have an actuator, built-in magnetic material is one option for robot operation (Yesin et al., 2005; Mathieu et al., 2006). A controlled magnetic field gives the robot linear and rotational momentum. Applying a rotational magnetic field to a permanent magnet placed inside a robot (Tomie et al., 2005) makes the robot spin and move wirelessly. However, mobile phones or metal items can cause the robot to move unexpectedly. The use of an internal medical robot equipped with a permanent magnet could thus be detrimental to patient health.

Another option is the use of built-in ferromagnetic material. A strong external magnetic field would guide robot travel, but magnetic forces caused by mobile phones and metal items would not be strong enough to move the robot. Such a design would avoid unexpected movement that could endanger patient well-being.