Optimal design of bone tumor ablation device based on radio frequency heating using Taguchi method.

This study investigated the optimal design of a radio-frequency (RF) bone tumor ablation device to achieve uniform heating. In a previous study, we confirmed the feasibility of this device, which could heat all regions of the bone to 70 °C or higher and maintain this temperature for more than 30 min. However, the temperature in each part was non-uniform. To address this issue, the shape of the electrode must be modified to create a uniform electric field. The design of the electrode was optimized to reduce temperature deviations. It is difficult to analytically model the relationship between the shape of the electrode and the electric field. The electrode's design factors were fine-tuned using the Taguchi method, a robust design of experiment approach. The primary objective in this optimization was to maximize the signal-to-noise ratio for temperature in each component, aiming for higher values. After four trials, the signal-to-noise ratio increased in comparison with the initial modified shape from 68.3 to 98.6. The experiment was conducted using an experimental device fabricated using the optimal design factors. In comparison to the previous experiment, the temperature standard deviation per part over time decreased from 10.56 °C 4.28 °C. The experimental results demonstrated the validity of the proposed optimal design approach. In the future, the proposed method can be used to optimize the design factors when a product is advanced to develop a device that can be applied to the human body.

Feasibility of a Novel In-situ Local Tumor Ablation and Recycling Machine Based on Radiofrequency Dielectric Heating: In-depth Review on Research Background and Preliminary Report of an Experimental Study.

Background: In bone sarcomas, chemotherapy has improved the prognosis with advances in diagnostic and surgical technologies, which has led to attempts to save limbs. As early detection and multidisciplinary treatment have improved the survival rate, curative surgery is considered for selected patients with metastatic bone carcinomas. Limb salvage procedures may vary in relation to the reconstruction method, which is accompanied by different complications. To overcome them, we devised a novel concept, in-situ local tumor ablation and recycling machine based on radiofrequency (RF)-induced heating and intended experiments to demonstrate its feasibility. Methods: The fresh femurs of 6-month-old pigs were used after removing the epiphyses; the distal parts were placed in a heating chamber. Fiber-optic temperature sensors were inserted in the metaphysis, meta-diaphysis, and diaphysis. Temperatures were measured six times each during heating at 27.12 MHz at various powers. Additionally, the compressive and bending stiffnesses were measured six times each for the unprocessed, RF-treated, and pasteurized bones, and the results were compared. Results: Under 200 W power output, the temperatures at all measurement sites reached 70 ℃ or higher in 6 minutes, and the temperatures were maintained. The median compressive stiffness of RF-heated bones was 79.2% higher than that of pasteurized bones, but the difference was statistically insignificant. The median bending stiffness of RF-heated bones was approximately 66.3% of that of unprocessed bones, which was 20% higher than that of pasteurized bones. Conclusions: The feasibility to rapidly attain and maintain temperatures for tumor ablation is shown, which favorably preserves bone stiffness through the in-situ local tumor ablation and recycling based on RF heating. The problem of nonuniform temperature distribution might be solved by an optimal design determined from simulation research and additional experiments.

Soft tissue surgical robot for minimally invasive surgery: a review.

Purpose: The current state of soft tissue surgery robots is surveyed, and the key technologies underlying their success are analyzed. State-of-the-art technologies are introduced, and future directions are discussed. Methods: Relevant literature is explored, analyzed, and summarized. Results: Soft tissue surgical robots had rapidly spread in the field of laparoscopic surgery based on the multi-degree-of-freedom movement of intra-abdominal surgical tools and stereoscopic imaging that are not possible in conventional surgery. The three key technologies that have made surgical robots successful are wire-driven mechanisms for multi-degree-of-freedom movement, master devices for intuitive remote control, and stereoscopic imaging technology. Recently, human-robot interaction technologies have been applied to develop user interfaces such as vision assistance and haptic feedback, and research on autonomous surgery has begun. Conclusion: Robotic surgery not only replaces conventional laparoscopic surgery but also allows for complex surgeries that are not possible with laparoscopic surgery. On the other hand, it is also criticized for its high cost and lack of clinical superiority or patient benefit compared to conventional laparoscopic surgery. As various robots compete in the market, the cost of surgical robots is expected to decrease. Surgical robots are expected to continue to evolve in the future due to the need to reduce the workload of medical staff and improve the level of care demanded by patients.

Real-time UVMS torque distribution algorithm based on weighting matrix.

This study presents a real-time algorithm for even distributing the torque burden on the parallel manipulator with an autonomous underwater vehicle (AUV) through the cooperation of the AUV and manipulator. For the redundant resolution of the underwater vehicle manipulator system (UVMS), we used the weighting matrix of the weighted pseudo inverse for kinematic and dynamic modeling. We made dynamic and kinematic modeling using the force distribution characteristics of parallel manipulators. Using the parallel manipulator's model, the weighting matrix was changed every second to share the manipulator torque with the AUV. The Taguchi method was used to reduce the calculation time for real-time calculation and to perform valve rotation operations with as little torque as possible even in an underwater environment where it is difficult to determine any cause of errors. To demonstrate the effectiveness of this algorithm, we experimented with valve rotation in water using the UVMS. Analysis of the experimental results revealed that the manipulator torque load was greatly reduced due to the AUV load distribution.

Force-Free Control for Direct Teaching of a Surgical Assistant Robot End Effector with Wire-Driven Bidirectional Telescopic Mechanism.

This paper shows the design and modeling of an end effector with a bidirectional telescopic mechanism to allow a surgical assistant robot to hold and handle surgical instruments. It also presents a force-free control algorithm for the direct teaching of end effectors. The bidirectional telescopic mechanism can actively transmit force both upwards and downwards by staggering the wires on both sides. In order to estimate and control torque via motor current without a force/torque sensor, the gravity model and friction model of the device are derived through repeated experiments. The LuGre model is applied to the friction model, and the static and dynamic parameters are obtained using a curve fitting function and a genetic algorithm. Direct teaching control is designed using a force-free control algorithm that compensates for the estimated torque from the motor current for gravity and friction, and then converts it into a position control input. Direct teaching operation sensitivity is verified through hand-guiding experiments.

Switching PD-based sliding mode control for hovering of a tilting-thruster underwater robot.

This paper presents a switching PD-based sliding mode control (PD-SMC) method for the 6-degree-of-freedom (DOF) hovering motion of the underwater robot with tilting thrusters. Four thrusters of robot can be tilted simultaneously in the horizontal and vertical directions, and the 6-DOF motion is achieved by switching between two thruster configurations. Therefore, the tilting speed of thruster becomes the most essential parameter to determine the stability of hovering motion. Even though the previous PD control ensures stable hovering motion within a certain ranges of tilting speed, a PD-SMC is suggested in this paper by combining PD control with sliding mode control in order to achieve acceptable hovering performance even at the much lower tilting speeds. Also, the sign function in the sliding mode control is replaced by a sigmoid function to reduce undesired chattering. Simulations show that while PD control is effective only for tilting duration of 600 ms, the PD-based sliding mode control can guarantee the stable hovering motion of underwater robot even for the tilting duration of up to 1500 ms. Extensive experimental results confirm the hovering performance of the proposed PD-SMC method is much superior to that of PD method for much larger tilting durations.