Wheekuk Kim

RCC Characteristics of Planar/Spherical Three Degree-of-Freedom Parallel Mechanisms With Joint Compliances

A three degree-of-freedom (DOF) planar parallel manipulator has been extensively studied as the fundamental example of parallel manipulators. In this work, we explicitly show that this mechanism possesses a completely decoupled compliance characteristic at the object space, which is the important operational requirement for a RCC device. As the first condition to have a RCC point, this mechanism should maintain symmetric configurations. As the second condition, the same magnitude of revolute joint compliance should be symmetrically placed at the same joint location of each chain. We also investigate the compliance characteristics of a spherical 3 DOF mechanism which has a similar kinematic structure to the planar mechanism through simulation. It turns out that the spherical mechanism also has a RCC point at the intersection point of all nine joint axes in its symmetric configuration. Further, more general output compliance model is derived for those mechanisms with redundant joint compliances. It is expected that these two parallel mechanisms not only can be used as excellent 3 DOF RCC devices, but also can be integrated into the design of a new six DOF RCC device.

A robot-assisted surgery system for spinal fusion

The goal of this work is to develop a robot-assisted surgery system for spinal fusion, which is composed of a robot, a surgical planning system, and an optical tracking system. The system plays roles of assisting surgeon for inserting a pedicle screw in spinal fusion. Compared to pure navigation systems as well as conventional methods for spinal fusion, it is able to achieve better accuracy through compensating for the portending movement of the surgical area. Furthermore, the robot can position and guide needles, drills, and other surgical instruments or conducts drilling/screwing directly. In preoperative surgery, the desired entry point, orientation, and depth of surgical tools for pedicle screw insertion are determined by the surgical planning system based on CT or MR images. Intra-operatively, the position information on the surgical instruments and the targeted surgical areas are obtained by the tracking system and, using that information, a robot conducts the preplanned operation depending on its role while compensating the movement of the surgical area. Two exemplary experiments employing the developed robot-assisted surgery system are conducted.

Multi-task oriented design of an asymmetric 3T1R type 4-DOF parallel mechanism

In performing tasks requiring less than 6 degrees-of-freedom (DOF), lower mobility robots having a parallel structure are effective. This work investigates an asymmetric type 4 degrees-of-freedom parallel mechanism having Schönflies motions. This mechanism would be useful for multi-purpose tasks because it incorporates a transmission linkage with appropriate output modules. The mobility analysis, kinematic modelling, and singularity analysis for the mechanism are performed. Optimal design parameters with respect to both the workspace size and kinematic isotropy are identified by employing composite global design index. In addition, to cope with the singularity problem, a new design involving redundant actuation is suggested. And dynamic simulations are conducted to reaffirm its high potential in real manufacturing applications.

Design of a new gravity balanced parallel mechanism with Schönflies motion

In this paper, a new gravity-balanced 3T1R parallel mechanism is addressed. Firstly, structure description, inverse and forward kinematic modeling are performed in detail. Secondly, Jacobian derivation based on screw theory and singularity analysis using Grassmann Line Geometry is performed, and then optimal kinematic design with respect to workspace size, kinematic isotropy and maximum force transmission ratio are conducted. Thirdly, the gravity balancing design using both counterweights and springs is proposed and a prototype of this mechanism is also presented. Results of analysis show that the proposed mechanism has quite a few potential applications.

Kinematic analyses of a 1T2R and a 1T3R parallel mechanisms with closed-form position solutions

Two parallel mechanisms, a 1T2R (one translational motion and 2-DOF rotational motions) and a 1T3R (one translational motion and 3-DOF spherical motion), are proposed. The 1T2R mechanism consists of three sub chains. Specifically, the middle sub chain has a similar joint arrangement with a PRR serial mechanism. Two revolute joints located at the top plate are driven by two closed-chain linkages. Similarly, the 1T3R mechanism employs the same concept as the 1T2R mechanism. The 1T3R has one more closed linkage to actuate the distal revolute joint of a PRRR serial sub chain in the middle. Due to these linkage arrangements, both of these two mechanisms have closed-form forward and inverse position solutions. Kinematic modeling of these two mechanisms is performed and their kinematic analyses are investigated with respect to their workspace and kinematic isotropic characteristics. Finally, to verify the motion capability of the mechanisms, their simulators are developed.

Trajectory planning in 6-degrees-of-freedom operational space for the 3-degrees-of-freedom mechanism configured by constraining the Stewart Platform structure

When the Stewart Platform mechanism is modified to have three RRPS type struts each of which is assumed to have an active prismatic joint and to be constrained by an additional serial passive PPPRRR type subchain, the modified mechanism could be reconfigured as one of various types of the non-redundant 3-degree-of-freedom mechanisms depending on which three joints of the passive PPPRRR subchain are locked and unlocked during real operation. This type of modified Stewart Platform mechanisms manifest a distinctive feature: that is, the modified mechanism could be reached to whole six-degree-of-freedom output workspace by properly controlling lock and unlock conditions of the corresponding number of joints among six passive joints of a PPPRRR serial subchain only with three active prismatic joints in struts. In this paper, this advantageous feature is investigated and verified through simulation. For that purpose, trajectory planning of the modified 3-degrees-of-freedom Stewart platform mechanism in static environments where obstacles are sparsely placed is studied. The objective of the trajectory planning is to find the path which could maintain good kinematic isotropic property while avoiding obstacles and switch to better 3-degrees-of-freedom configurations along the trajectory if necessary, for the given both initial and final configurations of the robot in six-degrees-of-freedom operational space. To find such a path, Q-learning algorithm which is one of reinforcement learning methods is employed.

Kinematic Analysis and Motion Planning for a Planar Multiarticulated Omnidirectional Mobile Robot

In this paper, kinematic modeling and singularity analysis are performed for an omnidirectional mobile robot. At the beginning, generalized formulas of the mobility and the first-order kinematics for a planar multiarticulated omnidirectional mobile robot are proposed. To verify the proposed formulas, a mobile robot that consists of three wheel mechanisms each of which has one redundant joint as compared to the operational degrees is introduced. Initially, the kinematic modeling and dynamic analysis, and odometry calculation for this robot are conducted. Next, singularity analysis of the proposed robot is performed. Then, using such a kinematic redundancy of each chain, motion planning algorithms that exploit the kinematic redundancy of the wheel chain are suggested. For navigation, a localization algorithm of the mobile robot based on odometry is presented, and specifically, two-leveled obstacle avoidance scheme, which simultaneously considers both large and small obstacles, is proposed. The usefulness of the proposed algorithms is verified through experimentation.

Synthesis of new statically balanced parallel mechanisms

In this paper, a method for type synthesis of several new statically balanced parallel manipulators is presented systematically. Firstly, using the concept of constant potential energy, we propose a statically balanced stackable planar mechanism. Secondly, based on the statically balanced stackable planar mechanism, independent statically balanced limb types with certain constraint are designed. Thirdly, combining specific limbs with different wrench system, we synthesize several n-DOF (degree of freedom) parallel mechanisms.

Automation of Surgical Illumination System Using Robot and Ultrasonic Sensor

Most surgery illumination systems have been developed as passive system. However, sometimes it is inconvenient to relocate the position of the illumination system whenever the surgeon changes his pose. To cope with such a problem, this study develops an auto-illumination system that is autonomously tracking the surgeons movement. A 5-DOF serial type manipulator system that can control (X, Y, Z, Yaw, Pitch) position and secure enough workspace is developed. Using 3 ultrasonic sensors, the surgeons position and orientation could be located. The measured data are sent to the main control system so that the robot can be auto-tracking the target. Finally, performance of the developed auto-illuminating system was verified through a preliminary experiment in the operating room environment.

Design of an Omnidirectional Mobile Robot with 3 Caster Wheels

Abstract In this paper, design of a 3-degree-of-freedom mobile robot with three caster wheels is performed. Initially, kinematic modeling and singularity analysis of the mobile robot is performed. It is found that the singularity can be avoided when the robot has more than two wheels on which two active joints are located. Optimal kinematic parameters of mobile robots with three active joint variables and with four active joint variables are obtained and compared with respect to kinematic isotropic index of the Jacobian matrix of the mobile robot which is functions of the wheel radius and the length of steering link.