Jungyun Kim

Singularity Analysis of Closed Kinematic Chains

This paper presents a coordinate-invariant differential geometric analysis of kinematic singularities for closed kinematic chains containing both active and passive joints. Using the geometric framework developed in Park and Kim (1996) for closed chain manipulability analysis, we classify closed chain singularities into three basic types: (i) those corresponding to singular points of the joint configuration space (configuration space singularities), (ii) those induced by the choice of actuated joints (actuator singularities), and (iii) those configurations in which the end-effector loses one or more degrees of freedom of available motion (end-effector singularities). The proposed geometric classification provides a high-level taxonomy for mechanism singularities that is independent of the choice of local coordinates used to describe the kinematics, and includes mechanisms that have more actuators than kinematic degrees of freedom.

Manipulability of Closed Kinematic Chains

This paper presents a coordinate-invariant differential geometric analysis of manipulability for closed kinematic chains containing active and passive joints. The formulation treats both redundant and nonredundant mechanisms, as well as over-actuated and exactly actuated ones, in a uniform manner. Dynamic characteristics of the mechanism and manipulated object can also be naturally included by an appropriate choice of Riemannian metric. We illustrate the methodology with several closed chain examples, and provide a practical algorithm for manipulability analysis of general chains.

On the energy efficiency of CVT-based mobile robots

We perform an in-depth analysis on the energy efficiency of a mobile robot employing a spherical type continuously variable transmission (S-CVT). The S-CVT permits the motor to operate in its most power-efficient regime of high-speed and low-torque, and allows for smooth operation of the mobile robot in all phases of forward, neutral, and reverse motion without the use of any brakes or clutches. Changes in steering direction are achieved by a novel pivoting device that enables the robot to rotate about its center. The current study takes into account features of the DC motors, the S-CVT, and the mobile robot dynamics to perform a comprehensive study on the overall system performance. We develop optimal control laws for both the reduction gear unit and S-CVT equipped mobile robots, and compare their energy efficiency through numerical studies. We then present numerical results that demonstrate the power savings possible front the use of the S-CVT mechanism over standard reduction gear units.

Direct kinematic analysis of 3-RS parallel mechanisms

Abstract This article presents a direct kinematic analysis of 3-RS parallel mechanisms. A 3-RS parallel mechanism consists of a fixed base and a moving platform connected by three serial chains, with each serial chain containing one passive revolute joint and one passive spherical joint. A variety of 3-RS mechanisms have been proposed in the literature, to overcome the disadvantages of small workspace characteristic of Stewart platforms and other 6–6 parallel mechanisms. We provide a computationally efficient method to solve the direct kinematics problem for general 3-RS mechanisms. By appealing to Sylvesters dialytic elimination method, the direct kinematics problem can be reduced to the solution of a 16th order polynomial equation in a single variable. In our approach the polynomial coefficients are represented in terms of convolutions of vectors, which considerably simplifies the coding of the algorithm, and unlike existing approaches does not rely on symbolic computation software. The method is applied to the direct kinematic analysis of the Eclipse, a novel six d.o.f. 3-RS parallel mechanism designed for five-face machining.

Design and Analysis of a Spherical Continuously Variable Transmission

In this article we propose the design of a novel continuously variable transmission, the spherical continuously variable transmission (S-CVT). The S-CVT consists of a sphere, input and output discs, and variators. The rotating input and output discs are connected to the power source and output shafts, respectively, while the sphere is situated between the input and output discs. The transmission ratio is controlled by adjusting the location of the contact point between the variators and the sphere, which in turn controls the axis of rotation of the sphere. The S-CVT can smoothly transit between the forward, neutral, and reverse states without any brakes or clutches, and its compact and simple design and its relatively simple control make it particularly effective for mechanical systems in which excessively large torques are not required (e.g., mobile robots, household appliances, small-scale machining centers). We describe the operating principles behind the S-CVT, including a kinematic and dynamic analysis. Simulations and experiments with a constructed prototype are conducted to assess the performance of the S-CVT, including a study of its energy efficiency vis-a-vis reduction gears.

Design, Analysis and Control of a Wheeled Mobile Robot with a Nonholonomic Spherical CVT

This article reports on the design, analysis and control of a new type of wheeled mobile robot based on a nonholonomic spherical continuously variable transmission (S-CVT). Our S-CVT based mobile robot is designed to increase the run time (i.e., the length of time in which the robot can be operated), and to achieve full planar accessibility with the design of a novel pivoting device that takes advantage of the flexibility of the S-CVT. We examine the sources of power loss in the S-CVT, in particular spin loss. For a quantitative analysis of spin loss of the S-CVT, we develop a friction model for the S-CVT, and perform an in-depth contact analysis based on the relative velocity field and normal pressure distribution. We also present a nonlinear shifting controller based on feedback linearization that takes into account the dynamics of the S-CVT. To evaluate the energy efficiency of our mobile robot and the performance of the S-CVT as a machine element, we perform experiments with a hardware prototype. The results are benchmarked numerically with a differential drive type mobile robot equipped with a reduction gear.

MOSTS: a mobile robot with a spherical continuously variable transmission

Introduces the design and analysis of a type of wheeled mobile robot that uses a spherical continuously variable transmission (S-CVT) element. The S-CVT is composed of a sphere, input and output discs, and variators, and power transmission is based on the friction force between the discs and the sphere. Use of the S-CVT allows for smooth operation of the mobile robot over all phases of forward, neutral, and reverse motion without the use of any brakes or clutches. The S-CVT also permits the motors to operate in their most power-efficient regimes. Motion in the plane, including pure rotation about its center is achieved by a novel pivoting device that eliminates the need for an actuated steering wheel, or an additional motor for differentiating the wheel velocities. We describe the conceptual principle behind our CVT-based mobile robot, and present a complete design and analysis of its capabilities based on a prototype currently under construction.

Eclipse-RP: a new RP machine based on repeated deposition and machining

Abstract This paper presents a newly developed rapid prototyping (RP) machine. The design of this machine is based on the Eclipse parallel mechanism invented by the authors. One of the advantages of the Eclipse mechanism as compared to Gough-Stewart-based parallel mechanisms and applied to machining processes is that the spindle can tilt to 90 degrees and enables five-face machining without any set-up change of the workpieces. This advantage has been fully utilized in designing the new RP machine. The RP process consists of four stages: (1) post-machining feature extraction, (2) the slicing of the deposition feature, (3) repeated deposition and machining of each sliced layer, and (4) post-machining. Whole stages are executed in one machine structure without any set-up change. Using the Eclipse-RP and standard test parts, remarkable gains in productivity are obtained, namely 2.5 times reduction in time and 8 times reduction in cost.

Analysis of Agricultural Working Load Experiments for Reduction Gear Ratio Design of an Electric Tractor Powertrain

Recent environmental issues such as exhaust gas and greenhouse effect make the agricultural machinery market takes into account the hybrid and electric propulsion technology used in automotive engineering. Generally the agricultural machinery, particularly an agricultural tractor, needs large load capacity and long continuous operating time comparing with conventional vehicles. In case of a pure electric tractor, it is necessary for considering large capacity batteries and long charging time. Therefore we take an AER extended PHEV (All Electric Range extended Plug-in Hybrid Electric Vehicle) power transmission system in developing an electric tractor in this study. First we propose a PHEV powertrain structure in order to substitute the conventional diesel engine equipped tractor. And we performed the road tests using a conventional mechanical tractor with various load conditions, which were classified and statistically treated real agricultural works. The test results were analysed with respect to the power characteristics of the power source. Finally using the test result, we designed two-stepped reduction gear ratios in the proposed an electric tractor powertrain for carrying out typical agricultural works.

Dynamic Performance Analyzing of In-wheel Vehicle considering the Real Driving Conditions and Development of Derivation System for Applying Dynamometer Using Drive Motor's Dynamic Load Torque

Abstract : This paper discusses about analyzing in-wheel vehicle’s dynamic motion and load torque. Since in-wheel vehicle controls each left and right driving wheels, it is dangerous if vehicle’s wheels are not in a cooperative control. First, this study builds the main wheel control logic using PID control theory and evaluates the stability. Using Carsim-Matlab/Simulink, vehicle dynamic motion is simulated in virtual 3D driving road. Through this, in-wheel vehicle’s driving performance can be analyzed. The target vehicle is a rear-wheel drive in D-class sedan. Second, by using the first In-wheel vehicle’s performance results, it derivate the drive motor’s dynamic load torque for applying the dynamometer. Extracted load torque impute to dynamometer’s load motor, linear experiment in dynamometer can replicated the 3-D road driving status. Also it, will be able to evaluate the more accurate performance analysis and stability, as a previous step of actual vehicle experiment. Key words : Inwheel(인휠), Carsim(카심), Driving performance(주행 성능), Load torque(부하 토크), Dynamo-meter(동력 시험계)