The trend of achieving minimal invasiveness in surgeries and recent technological advances in robotics have resulted in the emergence of flexible surgical robots. Such flexible robots can reach a surgical site via narrow and tortuous pathways, extending the reach of robotic surgery and potentially reducing the incision size. This review covers the key technical issues associated with flexible surgical robotics and introduces emerging flexible surgical robot systems organized according to their target applications in the endoluminal surgical field. Furthermore, the challenges and recent advancements in manipulator design, modeling, and control as well as the shape and force sensing of flexible robots are presented as key technical issues. Furthermore, the technical features and clinical values of emerging flexible surgical robot systems are introduced with their medical applications.

We have developed two technologies for 3D magnetic microstructures, with a wide size range between 5μm to 2mm. The first technology enables us to obtain density controlled 3D magnetic microstructures. The size of this structure is approximately 500μm. In this scale, controlling density is vital for magnetic micro actuators, because the effect of gravity is strong. To adjust density, we developed the world's first “density controllable magnetically photocurable (DMPC) polymer.” The DMPC polymer is a mixture of hollow microcapsules (density, 0.03 g/cm3), magnetic particles, and photocurable polymer. We can obtain desired relative density between 0.5 to 1.7 by adjusting the concentration of microcapsules. In addition, we succeeded in 3D velocity control of a screw-type magnetic micro actuator with neutral buoyancy in water. The delay time was 32msec, which is smaller than video rate. In addition, the actuator possessed 6 degrees of freedom. The second technology realized a 5μm magnetic micro actuator, which is a combination of a 3D transparent structure and 2D magnetic structure. Various photocurable polymers can be applied as the 2D structure in this process, although we used magnetically photocurable polymer in this report. Furthermore, we have succeeded in driving a ferromagnetic micro actuator, whose diameter is as small as 1μm. These two fabrication processes will become key technologies in both the medical field and the field of life sciences, because they can supply a wide variety of 3D micro structures with small effort.

We aimed to develop an active catheter that could be used safely in human blood vessels. We proposed and developed a micro valve for a water pressure-driven system with multi-degrees of freedom, to produce an active catheter that is compact and not driven electrically. In this paper, we proposed a new method that uses pressure pulses to control the bending angle of the active segment. We experimentally verified this control method using the new valve design.

The world's smallest micro active catheter of φ∼300µm was successfully fabricated using membrane micro emboss following excimer laser ablation (MeME-X) process. The catheter has a one-sided hollow bellows at the tip made of thin polymer membrane. The bellows is composed of a series of folded micro-chambers and microchannels connecting the micro-chambers. The folded-chambers expand on one side by increasing inner water pressure using a syringe, thus the whole bellows bends toward one direction within 0 to 180 degree. This micro active catheter should be useful for safe intravascular surgery in narrow and complicated blood vessels. Moreover, the nonelectrical actuation mechanism of this catheter can be widely applied to micro-actuators and micro-robots which need high safety.

We aimed to develop an active catheter that could be used safely in human blood vessels. We proposed and developed a new type of micro valve and incorporated this into a hydraulic pressure drive system with multi-degree of freedom, to produce an active catheter that was compact and required no electrical power for operation. We experimentally verified the good operational performance of a prototype of this active catheter

A new robotic system named "Hyper Finger" for minimally invasive surgery in deep organs has been developed. The finger size of the latest version is 10 mm and the entire system is much smaller and lighter, and can be set up on a camera tripod. This is one of the smallest master-slave robots in medicine. Each finger has nine degrees of freedom and several unique mechanisms are employed to solve the fundamental issues of conventional wire drive manipulators. The new concept and system were verified successfully by in-vivo remote minimally invasive surgery. Further improvements of the system toward a clinical version are now underway.

We proposed and developed an innovative active catheter with multi-segments that can bend in the narrow blood vessel. Micro hydraulic actuator system based on new principle has been developed by the authors. Moreover, new three dimensional micro fabrication method named "hybrid stereolithography" (IH process) to make hybrid structure without any assemble process is utilized for miniaturization and leakage-free packaging of the active catheter. Diameter has reached to 1.5 mm at the latest version. Total system with pressure control system was made. Good safety and drive performance were verified experimentally. We also devised theoretical models of these valves to facilitate quantitative design and to extend applications for safe medical tools.

We developed both new operation procedure and new robot system for remote micro surgery at deep and narrow space of human body. This system allows us to operate a difficult microsurgery that conventional method cannot be achieved. Our system consists of flexible stem and slave micro manipulators which can enter deep site such as brain through narrow channel. The macro motion of master manipulator can be converted into miniature motion of the slave microsurgery manipulator with five degrees of freedom in 3 mm diameter. This system has been taking advantage of flexible catheter and decoupled micro manipulator invented by Ikuta. Total performance was verified by animal experiment.

We propose a safety-optimizing method for safety strategies of human-care robots using our danger evaluation method. First, various safety evaluation methods are discussed, and an optimizing method of safety design is proposed. Second, we make a comparative study of two general safety control methods, and then a method of optimizing robot control is proposed. These proposed methods enable us to optimally distribute cost among several safety strategies, and to derive suitable approaching motion of a multi-link manipulator to a human. The validity and effectiveness of these methods are demonstrated by numerical analysis. As a result, the design and control to increase safety are successfully obtained.

VR training system for endoscopic inspection of intestine has been investigated developed by the authors. A mobile total system for hospitals is developed. This "Potable VES" consists of a miniaturized haptic mechanism to provide force sensation to the doctor, microcomputer and LCD display. All of these components are built in tower-type computer case with handle. New mathematical model are formulated and implemented to simulate large deformable intestine and endoscope. Several doctors demonstrate effectiveness of this system for pre-clinical training of basic skill for noninvasive inspection.

Proposes a safety evaluation method for use in various kinds of control strategies for human-care robots. In the case of a careless collision between a robot and a human, impact force and impact stress are chosen as evaluation measures, and a danger-index is defined to quantitatively evaluate the effectiveness of each safety strategy used for control. As in a previous paper on safety design, this proposed method allows us to assess the contribution of each safety control strategy to the overall safety performance of a human-care robot. In addition, a new type of 3D robot simulation system for danger-evaluation is constructed on PC. The system simplifies to evaluate danger about both design and control of various kind of human-care robots to quantify the effectiveness of various safety strategies.

A "Portable Virtual Endoscope System" (Portable VES) with haptic ability is developed. This Portable VES can present not only computer graphical images of an internal view of a virtual intestine but also reaction force through the endoscope. Unlike previous VES, the Portable VES has a simpler drive mechanism to achieve haptic ability. A large deformable dynamical model of both intestine and endoscope are formulated and implemented in the Pentium based microcomputer. Simulation and basic performance for clinical training are verified successfully by several experiments.

This paper proposes the world's first general evaluation method of safety for human-care and medical robots. The safety values chosen are impact force and impact stress. The danger index and safety index are defined to make quantitative evaluation of the effectiveness of each safety strategy. Moreover, this proposed method enables us to know the contribution of each safety strategy to the overall safety performance of human-care robots. As a result, design optimization of safe robots is discussed successfully.

We have proposed a new concept for an active endoscope with hyper redundancy. This medical tool called "Hyper Endoscope" for minimally invasive surgery is driven by miniature cybernetic actuators. A dynamic model of the cybernetic actuator, taking into account its piezoelectric effect, is proposed and its detailed performance analyzed. Based on the result, a new technique to minimize the number of lead wires is proposed and verified experimentally. The frequency modulation velocity control with two lead wires as an analog control method has been perfected.

We develop a virtual endoscope system (VES) with force sensation to train inexperienced doctors and simulate operations that require special technical skills. In this paper we describe the force simulation mechanism employed by our VES and dynamical models of an endoscope and colon. The force simulation mechanism was developed with the use of four rubber rollers and differential gears. The simple structure of this mechanism enables easy control and stable linear and rotational drive of the endoscope, and we confirm its force simulation ability by several experiments. We also develop the dynamical models of an endoscope and colon to calculate reactive force that doctors receive from a colon in real-time, and we confirm the accuracy of these models by software simulation. We believe this system is adequate for training young doctors in endoscopic insertion.

A granulated broadband network (GBN) is proposed as an intermediate asynchronous transfer mode (ATM) based platform to be part of an evolution scenario toward B-ISDN. The GBN enables various types of services to be provided including 64-kb/s-based services and broadband services. In the GBN, information is transformed into ATM cells at subscriber line terminals or at customer premises and is transferred through ATM networks; consequently, the cost feasibility of a single-channel cell assembly/deassembly device is a significant factor in economically providing ATM-based conventional services and interworking between STM and ATM networks. Various virtual path capacities with a fine degree of granularity can be provided in a mesh structure between transit modes in the GBN. Economic feasibility studies of the GBN, by simulating on certain large-size real networks in the greater Tokyo area, indicate the possibility of a more than 50% cost reduction in transit networks.>

New types of miniature actuators so called cybernetic actuator for biomedical robotics are developed. The cybernetic actuator has four driving states: free, increasing, decreasing and lock. The state of free and lock provides safety characteristics for both human and mechanism by avoiding damage from overload. The rotary type and linear type of cybernetic actuators are designed and developed. Feasibility of both actuators is verified by experiments. Four driving states are confirmed and unique driving principle is verified successfully.>

Shape memory alloy (SMA) has great potential for microminiature actuators. The feasibility is discussed, and theoretical estimates based on scale effect are presented. Control schemes for microminiature SMA servoactuators are discussed, and a control scheme is proposed. Combined with electric resistance feedback and position feedback, it enables the author to control stiffness of SMA directly and to sense force without a force sensor. Experimental verifications are reported. The application of a miniature SMA actuator to a miniature clean gripper with position-force hybrid control for microelectronics manufacture is presented. Fabrication of a thin film micro SMA actuator is investigated.>

A control system for a shape memory alloy (SMA) servo actuator, and its application to a unique medical tool, are considered. It is thought that the electric resistance value of an SMA can be utilized to monitor the transformation of the SMA directly. Therefore, an antagonistic transformation control scheme using electric resistance feedback is proposed and is verified by several experiments. This control scheme reduces the open-loop hysteresis of an SMA actuator and improves greatly its robustness against heat disturbance due to changes in the cooling condition. Research into the application of the method in an active endoscope is reported. It consists of five segments of 13 mm diameter, 40 mm length each. The bending angle of each segment can be controlled individually from outside by using antagonistic electric resistance feedback without any motion sensors. A model for smooth insertion to the colon is verified.>