Yong-San Yoon

Triangulation of scattered data in 3D space

Abstract Triangular interpolants are widely used to construct smooth surfaces from scattered data in 3D. To apply smooth triangular interpolants, the input 3D points have to be triangulated. This paper presents an algorithmic procedure for 3D triangulation. Relevant algorithms and datastructures are described in detail. Existing methods of 2D triangulation are based on Thiessen polygonization, which is an optimal partitioning of a geometric domain. To obtain an optimal triangular grid on the domain, the max-min angle criterion is frequently used. As there is no domain for 3D points, a new criterion called the smoothness criterion is proposed.

Robot-assisted femoral stem implantation using an intramedulla gauge

This paper presents a gauge-based registration method, a femur-mountable robot for hip arthroplasty named ARTHROBOT, and the surgery procedure using this system. In the gauge-based registration, a reamer-shaped gauge is inserted into the femoral medulla for relative positional information of the femur to the robot. A mounting frame and a minirobot are then mounted on the patients femur for accurate machining. This gauge-based registration method drastically reduces the processes in preoperative planning by eliminating the need of computer tomography scanning or other image processing methods, compared to other robotic systems that are used for hip surgery. Also, this surgical system reduces damage to the femur because only the metaphyseal region of the femoral canal needs to be machined, while leaving the diaphyseal hard bone untouched. Experiments were performed on 18 composite bones and 12 pig bones. In the composite bone group, orientation (anterversion, varus/valgus and flexion/extension) errors were made at 0.13/spl deg//spl plusmn/0.77/spl deg/, 0.14/spl deg//spl plusmn/0.38/spl deg/, and -0.27/spl deg//spl plusmn/0.33/spl deg/, and the maximum position error was at 1.00 mm. In the pig bone group, orientation errors were made at -0.03/spl deg//spl plusmn/0.65/spl deg/, 0.31/spl plusmn/0.27/spl deg/, and -0.36/spl deg//spl plusmn/0.36/spl deg/, and the maximum position error was at 1.12 mm. Also, 93% of the gaps between the bone and the implant surface were under 0.25 mm. The developed system shows sufficient machining accuracy and precision for clinical application.

The mechanism and registration method of a surgical robot for hip arthroplasty

This paper presents the mechanism and surgical method for ARTHROBOT, a new surgical robot for hip arthroplasty. The robot is femur-mountable and capable of 4-DOF motion. It uses a new gauge-based registration method that utilizes measuring instrument consisting of a reamer-shaped block gauge and a distance-measuring device. This gauge-based registration method drastically reduces the processes in the preoperative planning by eliminating the need of inserting fiducial markers or CT scanning. From the preliminary performance evaluation, it is shown to have less than 0.3 mm machining error, which seems to be sufficiently accurate for clinical application. Since the system has low operating cost and is compatible to the conventional manual surgery, it is expected to be easily adaptable to surgical needs and practices in the operating room.

ARTHROBOT : a new surgical robot system for total hip arthroplasty

This paper presents mechanisms and control methods of a new surgery robot for total hip arthroplasty (THA). To minimize the disadvantages of the conventional registration method, a new gauge-based registration method has been proposed, and a 3-DOF robot has been developed that can be mounted on a femur The proposed surgical robot can operate along a pre-programmed path autonomously, in addition to allowing a surgeon to directly control the motion of the surgical robot with their experience and judgment during an operation. For this purpose, a master is attached to the surgical robot and admittance display is used in control. ARTHROBOT this new arthroplastic surgical robot system, is expected to be adaptable to surgical needs and practice in the operating room.

Primary stability of cementless stem in THA improved with reduced interfacial gaps.

Large interfacial gaps between the stem and the bone in cementless total hip arthroplasty may prevent successful bone ingrowth at the sites, and can also be a passage for wear particles. Furthermore, interfacial gaps between the stem and the bone are believed to compromise the primary stability of the implant. Thus, a broaching method that serves to reduce gaps is expected to give clinically preferable results. A modified broach system with a canal guide is introduced to enhance the accuracy of femoral canal shaping in comparison with the conventional broach system for a Versys fibermetal taper stem. The primary stability of the hip systems and the ratios of the stem surface in contact with the femur were measured in a composite femur model. With the conventional method, an average of 67% of the stem surface was shown to be in contact with the bone, and an average stem micromotion/migration of 35 microm 290 microm was observed under 1000 cycles of stair climbing loads. With the modified method, the stem-bone contact ratio significantly increased to 82% (p<0.05), and the average micromotion/migration reduced to 29 microm 49 microm, respectively (p<0.05 for migration). Our finite element models of the hip systems supported that the difference in micromotion could be attributed to the difference in interfacial contact. Interfacial gaps occurring with the conventional broach system were effectively reduced by the proposed method, resulting in improved primary stability.

Real-time dynamic simulation of quadruped using modified velocity transformation

The dynamic formulation using the velocity transformation modified to make it more efficient with the recursive calculations and removal of trivial calculations is applied to the real-time simulation of the quadruped. The proposed method turned out to be an O(N) algorithm for parallel structures and an O(N/sup 3/) algorithm for serial structures from the fact that the computation for the simulation of the quadruped is proportional to the number of legs and the cube of the DOF of a leg. Thus it may be most profitable for the quadruped model with decoupled tree structure because it has been demonstrated that the best O(N/sup 3/) algorithms are faster than the best O(N) algorithms for N<10. The results also show that the real-time simulation can be achieved on a personal workstation with the application of parallel computation.

Stabilization constraint method for torque optimization of a redundant manipulator

The minimization of the joint torques based on the /spl infin/-norm is proposed for the dynamic control of a kinematically redundant manipulator. The /spl infin/-norm is preferred to the 2-norm in the minimization of the joint torques since the torques of the actuators are limited by their maximum values in magnitudes. To obtain the minimum /spl infin/-norm torque solution, we devised a new method that uses the acceleration polyhedron representing the end-effectors acceleration capability. Usually the torque minimization has the instability problem for the long trajectories of the end-effector. To suppress this instability problem, an inequality constraint, named the stabilization constraint, is developed from geometrical relations between the desired end-effector acceleration and the acceleration polyhedron. The minimization of the /spl infin/-norm of the joint torques subject to the stabilization constraint is shown to improve the performances through the simulations of a 3-link planar redundant manipulator.

Statistical Analysis of Interfacial Gap in a Cementless Stem FE Model

In cementless total hip arthroplasty, a fair amount of interfacial gap exists between the femoral stem and the bone. However, the effect of these gaps on the mechanical stability of the stem is poorly understood. In this paper, a finite element model with various interfacial gap definitions is used to quantify the effect of interfacial gaps on the primary stability of a Versys Fiber Metal Taper stem under stair climbing loads. In the first part, 500 random interfacial gap definitions were simulated. The resulting micromotion was approximately inversely proportional to the contact ratio, and the variance of the micromotion was greater with a lower contact ratio. Moreover, when the magnitude of the micromotion was compared between the gap definitions that had contact at a specific site and those that had no contact at that site, it was found that gaps located in the proximal-medial region of the stem surface had the most important effect on the micromotion. In a second trial, 17 gap definitions mimicking a gap pattern that has been observed experimentally were simulated. For a given contact ratio, the micromotion observed in the second trial was lower than the average result of those in the first, where the gaps were placed randomly. In either trial, when the contact ratio was higher than 40%, the micromotion showed no significant difference (first trial) or a gentle slope (-0.24 mum% in the second trial) in relation to the contact ratio. Considering the reported contact ratios for properly implanted stems, variations in the amount of interfacial gap would not likely cause a drastic difference in micromotion, and this effect could be easily overshadowed by other clinical factors. In conclusion, differences in interfacial gaps are not expected to have a noticeable effect on the clinical micromotion of this cementless stem.

Behavior planning of an unmanned ground vehicle with actively articulated suspension to negotiate geometric obstacles

The behavior control method was usually adapted for controlling the suspension configuration which determines the traversability of the UGV with actively articulated suspension. In this paper, we proposed a method of configuration planning of the suspension without any detail geometric data of terrain. The terrain was estimated by the traces of each wheel and the behavior plans for the desired upper level behavior were set up against the constraints of the terrain. Also, an optimal suspension configuration was calculated based on the quasi-static stability and power consumption, and plans for the suspension behavior were made. Validity of the proposed method was checked by simulation using some off-the-shelf programs, and showed that the behavior planning without geometric features of terrain and simplification of the behavior planning for obstacle negotiation were possible.

In vitro study using cadavers for evaluation of a bone-mountable surgical robot system

This paper describes a bone-mountable surgical robot system for hip surgery and its in vitro experiments with cadavers. The system eliminates the need for obtaining CT scan data by adopting gauge-based, bone-mounting registration method and is designed to replace only the broaching procedure, which is known to be the most error-prone procedure in the manual surgery. The performance of this system is evaluated with specimen of six human cadavers. X-ray images and photographed image of femurs are utilized for measuring the difference between the implant and the anatomical axes. As this deviation implies how the gait pattern of the operated patient may be influenced by the surgery, the amount of deviation is used as the indicative of system performance. The nominal differences of anteversion angle, valgus-varus angle, and flexion-extension angle are 0.02/spl plusmn/2.73/spl deg/, 0.98 /spl plusmn/0.39/spl deg/ and 0.51/spl plusmn/0.87/spl deg/, respectively. In case of the change in leg length after the surgery, the nominal error is -0.88/spl plusmn/1.26 mm. Experimental results show that the performance of the developed system is comparable to other surgical robots that use preoperative planning with CT scan data.