Alan Mutka

A leg-wheel robot-based approach to the solution of flipper-track robot kinematics

This paper presents the method of solving kinematics of a flipper-track robot. A general kinematics framework based on the screw theory is introduced for the leg-wheel robots. Focusing on the contact point between a flipper and the ground surface, the flipper-track robot kinematics is presented with the equivalent hybrid leg-wheel robot kinematics. For a studied four flipper-track robot, several robot control modes and corresponding kinematics solutions are identified. The algorithm for robot posture and tracking control is presented respecting robots mechanical constraints. The kinematics and robot posture control were tested by simulation on a virtual robot in the MATLAB-ODE simulation environment.

Elliptical motion method for robust quadrupedal locomotion

In this paper we present a new elliptical motion method that allows integration of different walking gaits with Jacobian-based robot body kinematics. Implemented walk and trot gaits are controlled with a central pattern generator (CPG). By combining these gaits with robot kinematics, robot pose control is enabled during robot motion. The proposed method generates the elliptical type of foot motion independently of possible robot pose changes, which makes robot locomotion very robust to various disturbance effects (e.g. impact of uneven terrain, external forces, and sensor-guided changes of robot posture). The method was implemented and tested on the 13 degrees of freedom (DOF) four-legged robot. The results have confirmed that the robot maintains the desired walking gait while changing its pose in accordance with a task being executed.

Control system for reactor vessel inspection manipulator

In this paper a system for control and 3D visualization of a manipulator for weld inspection of nuclear reactor vessels is described. Based on a client-server TCP/IP software architecture, the presented control system enables an operator to perform the entire inspection procedure remotely over a network, avoiding exposure to dangerous radiation which is commonly present in nuclear reactor environments. The developed graphical user interface provides all necessary tools needed for planning robot scan trajectories, their verification on a virtual 3D model and execution on a remote robot. In addition, the weld inspection process can be observed in parallel on a virtual robot and reactor vessel model and on live video streams captured by two special cameras mounted on the robot.

Adaptive Control of Quadruped Locomotion Through Variable Compliance of Revolute Spiral Feet

In this article we present a novel mechanical design of a robot leg that possesses active and variable passive compliance properties. The hip and knee joints provide active compliance, while the variable passive compliance comes from the spiral foot spring, mounted on the ankle joint, which changes its stiffness by rotating and changing contact angle with the ground. The stiffness of the foot for various contact angles was identified experimentally by using the strength tester measurement system. The method for damping coefficient identification, based on the observation of energy losses during the stance phase of leg hopping motion, is described and used to obtain the foot damping model. The adaptation of spiral foot stiffness to varying ground stiffness is achieved by extracting a leg contact time from a feedback signal provided by a flex sensor mounted on the foot. The experiments on a single leg and quadruped platforms have confirmed that the presented spiral foot design provides stiffness adaptability, partial recovery of the energy from the previous hop and restriction of stance contact time, which are all necessary conditions to obtain more efficient quadruped locomotion.

Stabilizing a quadruped robot locomotion using a two degree of freedom tail

This paper investigates how to improve locomotion stability of a dynamical system composed of four spring-mass subsystems by using a tail-like inertial appendage. The paper presents a Denavit-Hartenberg parameterization based kinematic model combined with a Newton-Euler based dynamic model of a two degree of freedom tail. Impedance based leg control simplifies the leg motion so that it can be modeled as a damped spring-mass system. The tail presented in the paper is used as a counterweight, capable of shifting its center of mass so as to balance the body of the robot. To that end, a recursive algorithm that moves the tail in order to balance the robot is proposed. A realistic robot model is built in the Open Dynamic Engine environment and is used to conduct a series of tests proving the effectiveness of the proposed algorithm.

New Variable Passive-compliant Element Design for Quadruped Adaptation to Stiffness-varying Terrain

This paper presents the design of a novel variable passive-compliant (VPC) element utilized as a lower-leg implant of a fully electrically driven quadruped robot. It is designed as a slider-piston mechanism which ensures that the force produced during a foot-ground contact is directly perpendicular to the contact surface of an actuated revolute spring. In this way, by altering the stiffness of quadruped legs in a closed-loop manner, the VPC element enables the quadruped robot to adapt to varying terrain characteristics, ensuring a constant hopping frequency over a wide range of terrain-stiffness variations. The designed VPC element and its beneficial characteristics are described in detail. Mathematical relations are formulated that help to describe the influence of the VPC element during vertical hopping of a quadruped robot. The properties of the quadruped research platform with integrated VPC element were verified in simulation and through experiments.

Design and control of a four-flipper tracked exploration & inspection robot

We describe the design and control of a prototype of an exploration and inspection robot built as a four flipper/track mobile robot. It is equipped with on-board sensors including standard and thermovision cameras, gas and temperature detectors, etc. The robot maintains wireless video and audio communication with the operator. Its principal aim is to explore buildings, locate people caught in the accidents and detect potential sources of danger in abnormal conditions caused by flood, fire, earthquake or other natural and nonnatural disasters. The robot construction complies to the ATEX norms in order to minimize the risk of interventions of professional units (e.g. fire fighting, civil guard, police, military). Having four independently controlled tracks/flippers, the robot allows easy maneuvering and overtaking of obstacles (including steps). Although dominantly designed as a remote-controlled robot device, advanced control features such as roll-angle compensation and corridor/steps/door centering algorithms help the operator to navigate robot in a much easier and safer way.

Fast visual tracking and localization in multi-agent systems

In this paper an implementation of an algorithm for fast visual tracking and localization of mobile agents has been described. Based on an extremely rapid method for visual detection of an object, described localization strategy provides a real time solution suitable for the design of multi-agent control schemes. The agents tracking and localization is carried out through five differently trained cascades of classifiers that process images captured by cameras mounted on agents. In this way, each agent is able to determine relative positions and orientations of all other agents performing tasks in its field of view. The described localization method is suitable for applications involving robot formations. Performance of the proposed method has been demonstrated on a laboratory setup composed of two mobile robot platforms.

A Low Cost Vision Based Localization System Using Fiducial Markers

Abstract This paper investigates a mobile robot self-localization system based on fiducial markers which are placed on the ceiling. Recently there have been many articles related to path planning and coordination of mobile agents within an unknown environment. These algorithms demand dedicated (and often expensive) hardware that is capable of handling complex tasks in real time. In this paper, we have explored the possibility to realize an inexpensive and simple navigation system, based on passive fiducial markers, which are able to guide an autonomous mobile robot along a predefined path. Fiducial markers provide not only improved performance in runtime, but also much better identification and localization. Marker design based on circle shape is presented. Using a low-cost webcam and appropriate marker detection algorithm three features are determined: robot position, new movement direction and marker ID. Experimental results are presented at the end of the paper.

Design, modeling and control of a system for dynamic measuring of leg length discrepancy

This paper presents a system for dynamic measuring of leg length discrepancy (LLD). The system consists of two 3-RPS parallel manipulators with three degrees of freedom. Parallel manipulators have force sensors that determine the patients center of gravity (COG) displacement. By changing the height of the moving platform of the parallel manipulator, COG returns in its expected position. The difference between the heights of moving platforms equals the amount of LLD. Inverse kinematics of the 3-RPS parallel manipulator was performed. A virtual simulation system was made and tested in MATLAB/Simulink. The paper presents simulation results of the system operation.