TaeWon Seo

Tank-Like Module-Based Climbing Robot Using Passive Compliant Joints

This paper proposes an underactuated modular climbing robot with flat dry elastomer adhesives. This robot is designed to achieve high speed, high payload, and dexterous motions that are typical drawbacks of previous climbing robots. Each module is designed as a tread-wheeled mechanism to simultaneously realize high speed and high adhesive force. Two modules are connected by compliant joints, which induce a positive preload on the front wheels resulting in stable climbing and high payload capacity. Compliant joints also help the robot to perform various transitions. An active tail is adopted to regulate the preload of the second module. Force transfer equations are derived and stable operating conditions are verified. The stiffness coefficients of the compliant joints and the active tail force are determined optimally to satisfy the constraints of stable operation. The prototype two-module robot achieves 6-cm/s speed and 500-g payload capacity on vertical surfaces. The abilities of flat surface locomotion, internal, external, and thin-wall transitions, and overcoming various sized obstacles are validated through experiment. The principle of joint compliance can be adopted in other climbing robots to enhance their stability and transition capability.

Gait planning based on kinematics for a quadruped gecko model with redundancy

Recent research on mobile robots has focused on locomotion in various environments. In this paper, a gait-generation algorithm for a mobile robot that can travel from the ground to a wall and climb vertical surfaces is proposed. The algorithm was inspired by a gecko lizard. Our gait planning was based on inverse kinematics using the Jacobian of the whole body, where the redundancy was solved by defining an object function for the gecko posture to avoid collisions with the surface. The optimal scalar factor for these two objects was obtained by defining a superior object function to minimize the angular acceleration of joints. The algorithm was verified through simulation of the gecko model travelling on given task paths and avoiding abnormal joint movements and collisions.

High-payload climbing and transitioning by compliant locomotion with magnetic adhesion

This paper presents a new climbing robotic mechanism for high-payload climbing and wall-to-wall transitioning. Payload capacity and transition ability are very important in climbing-robot applications for heavy industries and construction industries. The proposed robotic platform consists of three magnetic tread-wheel modules that are connected by links with two compliant joints. The front compliant joints are passive type with a torsion spring, and the rear compliant joints are active type with torque-controlled motors. A torque-controlled tail is attached at the end of the third module. Various transitions are achieved by the compliant joints, which change shape depending on the external conditions. High payloads are achieved by the large contact area of three magnetic tread-wheel modules. Detailed design issues are presented with analyses of the design parameters. The robot can perform two internal and two external transitions against gravity and every possible transition in the side surface driving direction. The robot can carry 10 kg payloads on vertical surfaces and on a ceiling. The ability to overcome a 30 mm diameter obstacle on vertical surfaces is also verified by experiments. The proposed robotic platform is going to be used in heavy industries.

Dual Servo Control of a High-Tilt 3-DOF Microparallel Positioning Platform

This paper presents a precise positioning control of a microparallel positioning platform using a dual-stage servo system. The result of the research can be applied to dual-stage-type parallel machines for improving the positioning accuracy. The proposed platform adopts a dual-stage system that consists of three coarse actuators and three fine actuators to realize 3 degrees of freedom (DOF) motion. The 3-DOF motion of the end-effector is measured by a set of three linear sensors. Dynamic models for the coarse and fine actuators are derived by the system identification approach. The gain-scheduled multi-input multi-output (MIMO) controllers are synthesized based on the modeling. The MIMO controller is designed with a mixed-sensitivity criterion on tracking performance and positioning capability, and the design of the gain scheduler is based on the kinematics change. By integrating the controllers for two kinds of actuators, a dual servo controller can be developed based on the master-slave with decoupling structure. An antiwindup controller and a feedforward compensator are adopted to improve the performance. The successful performance of the synthesized dual servo controller is validated through experiments on tracking to guarantee submicrometer accuracy.

Optimal design and workspace analysis of a mobile welding robot with a 3P3R serial manipulator

Abstract This paper presents the design optimization of a mobile welding robot based on the analysis of its workspace. A welding robot has been developed to be used inside the double-hull structure of ships, and it shows good welding functionality. But there is a need to optimize the kinematic variables ensuring that the required welding functions inside the ships are satisfied. The task-oriented workspace, which is the workspace enabling specific rotations, has been defined in order to validate the welding ability of the robot, and incorporating the required rotational capabilities. To calculate the workspace, a geometric approach is adopted which considers the pitching and yawing angles simultaneously. Based on the workspace analysis, a scenario is compiled for considering a mass reduction, and a ratio between the design parameters and the workspace, with constraints on the workspace margins. The proposed optimization procedure is composed of two steps of coarse and fine searching. In the coarse searching step, a feasible parameter region (FPR) is defined, which satisfies the geometrical design constraints, and can be obtained without any considerations of the objective functions. In the fine searching step, the design parameters are determined by using the optimization technique of the conjugate gradient method in the overall FPRs. The suggested approach to calculating the task-oriented workspace, and the procedure of optimal design, are expected to be applied to general industrial robots.

Water and Ground-Running Robotic Platform by Repeated Motion of Six Spherical Footpads

Bioinspired robotic platforms are based on knowledge from nature. Most robots focus on a single type of locomotion, such as walking or flying. However, multilocomotive robots have recently attracted considerable attention from researchers. In this study, an amphibious robotic platform was developed for operating on water and ground surfaces with a single design. The robot uses spherical footpads to remain on the water surface based on buoyancy and drag forces. Ground walking is also achieved by repeated tripod motion of the spherical footpads. Klann mechanism was adopted and optimized to achieve the footpad motion for stable locomotion on both surfaces. The velocity and pitching angle were analyzed by simulation and experiments at various operating frequencies to validate the performance of the platform. This robot could be applied in nuclear power plant accidents after hydrodynamic-force-based steering by the tail is achieved.

Six-Degree-of-Freedom Hovering Control of an Underwater Robotic Platform With Four Tilting Thrusters via Selective Switching Control

We introduce a new underwater robotic platform with a tilting thruster mechanism for hovering motion. The tilting thruster mechanism can implement six-degree-of-freedom (DOF) motion with only four thrusters, but tilting motion makes the system nonlinear. We designed a selective switching controller in order to solve the nonlinear problem, and applied it to the robot system. The selective switching controller divides the six-DOF system into two three-DOF subsystems, and switches between subcontrollers according to the error in real time. Dynamic models of a robotic platform and a disturbance model of an attached manipulator are derived for the control design. Using simulation, the stability condition of control is determined, and the validity of the derived dynamic model of the robotic platform and manipulator is verified through comparison between simulation and experiment. A hovering experiment under a disturbance from the manipulator is performed to verify the robustness of the controller. The experimental results validate the successful hovering ability of the proposed robot.

Kinematic Analysis and Experimental Verification on the Locomotion of Gecko

This paper presents a kinematic analysis of the locomotion of a gecko, and experimental verification of the kinematic model. Kinematic analysis is important for parameter design, dynamic analysis, and optimization in biomimetic robot research. The proposed kinematic analysis can simulate, without iteration, the locomotion of gecko satisfying the constraint conditions that maintain the position of the contacted feet on the surface. So the method has an advantage for analyzing the climbing motion of the quadruped mechanism in a real time application. The kinematic model of a gecko consists of four legs based on 7-degrees of freedom spherical-revolute-spherical joints and two revolute joints in the waist. The motion of the kinematic model is simulated based on measurement data of each joint. The motion of the kinematic model simulates the investigated real gecko’s motion by using the experimental results. The analysis solves the forward kinematics by considering the model as a combination of closed and open serial mechanisms under the condition that maintains the contact positions of the attached feet on the ground. The motions of each joint are validated by comparing with the experimental results. In addition to the measured gait, three other gaits are simulated based on the kinematic model. The maximum strides of each gait are calculated by workspace analysis. The result can be used in biomimetic robot design and motion planning.

A Micro-positioning Parallel Mechanism Platform with 100-degree Tilting Capability

Abstract This paper presents a micro-positioning platform based on the unique parallel mechanism recently developed by the authors. The platform has a meso-scale rectangular shape whose size is 20 × 23 mm. The stroke is 5 mm for both the x - and y -axis and 100 degrees for the α -axis (the rotational axis along the x -axis). The platform is actuated by the three sets of two-stage linear actuators: a linear motor for rough positioning and a piezo actuator for fine positioning. The platform is already assembled. The detailed design issues, including the kinematic analysis, and the experimental results of the positioning measurements and control performance, are presented.

Under-actuated tank-like climbing robot with various transitioning capabilities

This paper presents a modular climbing robot connected by two passive compliant joints and featuring an active tail. The objective of this robot is to enable various internal and external transitions which are very challenging tasks for previously developed climbing robots. Realizing the transitions by an using under-actuated system without complex control is another contribution of this research. The robot is driven using a tread-wheel mechanism made of a flat sticky polymer to realize fast and robust climbing. Directional compliant joints are used between the two modules to increase the preload on each front wheel. An active tail is used at the end of the second module to compensate for the negative effects of the compliant joint forces. This combination of directional compliant joints and active tail also allows the robot to perform various internal and external transitions passively. The induced positive preload on the front wheels are analyzed and verified. Three types of internal transition and three types of external transition including a thin-wall transition are achieved by the robot prototype. The concept of the directional compliance with the active tail can be adopted to other climbing robots to enhance robustness and mobility.