Jae Chul Hwang

Bio: Jae Chul Hwang is an academic researcher from Seoul National University. The author has contributed to research in topics: Eclipse & Machining. The author has an hindex of 3, co-authored 5 publications receiving 277 citations.

Design and analysis of a redundantly actuated parallel mechanism for rapid machining

Abstract: This paper describes the design, construction, and performance analysis of the Eclipse, a redundantly actuated six-degree-of-freedom parallel mechanism intended for rapid machining. The Eclipse is a compact mechanism capable of performing five-face machining in a single setup while retaining the advantages of high stiffness and high accuracy characteristic of parallel mechanisms. We compare numerical and algebraic algorithms for the forward and inverse kinematics of a class of the Eclipse and formalize the notion of machine tool workspace. We also develop a simple method for the first-order elasto-kinematic analysis of parallel mechanisms that is amenable to design iterations. A complete characterization of the singularities of the Eclipse is given, and redundant actuation is proposed as a solution. The Eclipse case study demonstrates how diverse analytical tools originally developed in a robotics context can be synthesized into a practical design methodology for parallel mechanisms.

Eclipse II: a new parallel mechanism enabling continuous 360-degree spinning plus three-axis translational motions

Abstract: This paper presents the Eclipse II, a new six-degrees-of-freedom parallel mechanism, which can be used as a basis for general motion simulators. The Eclipse II is capable of x, y, and z axes translations, and a, b, and c axes rotations. In particular, it has the advantage of enabling continuous 360/spl deg/ spinning of the platform. We first describe the computational procedures for the forward and inverse kinematics of the Eclipse II. Next, the complete singularity analysis is presented for the two cases of end-effector singularity and actuator singularity. Finally, two additional actuators are added to the original mechanism to eliminate both types of singularity within the workspace.

Parallel mechanism structure for controlling three-dimensional position and orientation

Abstract: Disclosed is a parallel mechanism structure for controlling three-dimensional position and orientation. In the parallel mechanism structure according to the present invention, three links are connected to the main spindle of the mechanism and driven in vertical and horizontal direction, with a consecution that the main spindle connected to the three links achieves the six d.o.f motions. The structure includes three links comprised of a first link transferred along a circular vertical guide and second and third links transferred along corresponding rectilinear vertical guides and a circular horizontal guide on which the circular vertical guide and the two rectilinear vertical guides are horizontally transferred.

Hybrid rapid prototyping method performing both deposition and machining

Abstract: A rapid prototyping method performing both deposition and machining, the method comprising a main process cycle and an additional machining process, wherein the main process cycle comprises repetition of the steps of: (a) machining the backside of the sheet by roughing and fining; (b) reversing the backside-machined sheet by 180 degrees, applying an adhesive and depositing the sheet on another one; and (c) machining the front side of the sheet by roughing, fining, and boundary cutting, wherein the additional machining process comprises drilling, milling or grinding. The rapid prototyping method performing both deposition and machining according to the present invention includes a main process cycle, which is composed of backside machining step, sheet reversing and deposition step and front side processing steps, and an additional machining process 17, which is to process small feature segments and composed of drilling, milling or grinding. The present invention method decomposes the whole building material into three-dimensional segments to dramatically reduce the total building time, while the conventional method divides the whole building material into thin layers of a predetermined thickness.

Disturbance-rejection high-precision motion control of a Stewart platform

Abstract: A simple robust autodisturbance rejection controller (ADRC) in linkspace is proposed to realize high precision tracking control of a general 6 degrees of freedom (DOF) Stewart platform in this paper. In practice, the performance of the controlled system is limited by how to select the high-quality differential signal in the presence of disturbances and measurement noise. Moreover, unmodeled nonlinear friction provides degradation on the motion precision. So, a nonlinear tracking differentiator in the feedforward path and an extended states observer in the feedback path are designed to obtain high quality differential signal and the real action component of unknown disturbance signals including nonlinear friction without a precise mathematical model. The nonlinear PD (proportional derivative) controller is used to synthesize the control action to give a superior performance. Extensive simulations and experimental results are presented to verify the effectiveness and ease of engineering implementation of the proposed method. The developed ADRC controller is simple and directly intuitive to the practitioners.

A Geometric Theory for Analysis and Synthesis of Sub-6 DoF Parallel Manipulators

Abstract: Mechanism synthesis is mostly dependent on the designer's experience and intuition and is difficult to automate. This paper aims to develop a rigorous and precise geometric theory for analysis and synthesis of sub-6 DoF (or lower mobility) parallel manipulators. Using Lie subgroups and submanifolds of the special Euclidean group SE(3), we first develop a unified framework for modelling commonly used primitive joints and task spaces. We provide a mathematically rigorous definition of the notion of motion type using conjugacy classes. Then, we introduce a new structure for subchains of parallel manipulators using the product of two subgroups of SE(3) and discuss its realization in terms of the primitive joints. We propose the notion of quotient manipulators that substantially enriches the topologies of serial manipulators. Finally, we present a general procedure for specifying the subchain structures given the desired motion type of a parallel manipulator. The parallel mechanism synthesis problem is thus solved using the realization techniques developed for serial manipulators. Generality of the theory is demonstrated by systematically generating a large class of feasible topologies for (parallel or serial) mechanisms with a desired motion type of either a Lie subgroup or a submanifold.