Dong Hun Shin

Explicit Path Tracking by Autonomous Vehicles

We have suggested a novel approach to autonomously navigate a full sized autonomous vehicle that separately treats vehicle control and obstacle detection. In this paper we discuss the vehicle control that has enabled our autonomous vehicle to travel at speeds upto 20mph. We point out the limitations of existing schemes that restrict their consideration to kinematic models and show that it is possible to obtain an increase in performance through the use of approximate dynamical models that capture first–order effects. Our approach combines such a modeling philosophy with accurate feedback in world coordinates from sensors that have only recently become available. Experimental results of our implementation on NavLab, a modified van at CMU, are presented.

Motion planning for a mobile manipulator with imprecise locomotion

This paper presents a motion planning method for mobile manipulators for which the base locomotion is less precise than the manipulator control. In such a case, it is advisable to move the base to discrete poses from which the manipulator can be deployed to cover a prescribed trajectory. The proposed method finds base poses that not only cover the trajectory but also meet constraints on a measure of manipulability. We propose a variant of the conventional manipulability measure that is suited to the trajectory control of the end effector of the mobile manipulator along an arbitrary curve in three space. Results with implementation on a mobile manipulator are discussed.

Vehicle and Path Models for Autonomous Navigation

Most implementations on the Navlab have used a simple Virtual Vehicle specification to control the vehicle. The Virtual Vehicle is a low level instruction set that accepts conceptual commands and provides a clean separation between a navigation host and vehicle control, masking implementation details of the physical vehicle. While such a scheme is modular and allows various groups of researchers to easily implement their algorithms on the vehicle, the price is paid in terms of limited performance. This cost has been acceptable for most applications so far since they require speeds on the order of 1 mile per hour.

Path Generation for a Robot Vehicle Using Composite Clothoid Segments

Abstract : The response of an autonomous vehicle in tracking a reference path depends partly on the nature of the path. The condition for paths that are intrinsically amenable to follow are briefly presented, and then a method for the generation of amenable paths is proposed in this paper. Previous path generation methods have sought to simplify a path by using arcs, superarcs, polynomial curves, and clothoid curves to round corners, which result from poly- line fits through a given sequence of points. The developed method consists of two steps: First, a sequence of postures is obtained using given points, then each pair of neighboring postures is connected with three clothoid curve segments. In the second step, a completely general method to connect a path of clothoid curves between two completely arbitrary postures was not envisioned and method for a pair of adjacent postures was developed. By virtue of the property of clothoid curves, a generated path is continuous with respect to position, tangent direction, and curvature, and is linear in curvature. Aside from the properties innate to clothoid curves, the generated paths transition smoothly into turns, pass through all the way points, and sweep outside the corners. For interpolating around obstacles that are commonly inside the corner, these properties are especially useful.

Open-loop Velocity Control of Concrete Floor Finishing Robots

The twin trowel concrete floor finishing robot consists of a pair of trowels, each of which rotates four plastering blades, and does not have any mechanism like wheels for its locomotion. However, while leveling the concrete floor, it can move in any direction with the unbalanced friction forces occurring between the trowels and the floor, which are controlled by adjusting the posture of the trowels. For the motion control of the robot, this paper discusses the following: First, the typical velocity feedback control method is not dependable because of the difficulties of measuring the robot velocity; secondly, the friction force, which drives the robot, is modeled when the robot is in translation motion; thirdly, the friction force decreases as the robot velocity increases, thus resulting in a saturated velocity dependent on the posture of the trowel; finally, the saturated velocity enables us to control the motion of the robot only by adjusting the posture of trowels without any feedback about the robot velocity.

Open-loop velocity control of the troweling robot

The 2-trowel type concrete floor finishing robot can move in any direction and rotate without any mechanism such as wheels by adjusting the posture of trowels. It utilizes the unbalanced friction forces occurring between the rotary trowels and the floor. Since the quality of the smoothed and polished concrete floor is determined by plastering speed, we need to control the velocity of the robot. However, we cannot use the typical velocity control method because it is very difficult to measure the velocity of the robot, in contrast to the mobile robots with wheels. To overcome this difficulty, the following are studied in the paper. We found that the robot dynamics has disturbance depending on its velocity, and showed that there exists the saturated velocity of the robot which is set by the posture of the trowels, and obtained the relationship between the saturated velocity and the posture in the translation and the rotation. These enable us to control the velocity of the robot only by adjusting the posture of trowels. We built the trowelling robot and are experimenting its performance with the proposed velocity control method.