Mircea Nitulescu

Theoretical aspects in wheeled mobile robot control

This work presents some considerations regarding mathematical models and control solutions for a class of mobile robots namely two-wheeled differential drive mobile robots, one of the most utilized mechanical structures now in mobile robotics practice. The closed loop control diagrams for position control and respectively for direction control in tracking along imposed trajectories are developed, analyzed and included in this paper. For these control solutions, the paper presents therefore some analyses regarding the stability in different circumstances. In addition, direct and inverse cinematic models for this class of mobile robots are included.

Mobile Robot Tracking Control Experiments along Memorized Planed Trajectories

This paper presents and analyses some results in path tracking control on complex plane trajectories for a differential wheeled mobile robot with memorized trajectories. The path planning and the path tracking control play an important role in control performance of mobile robots, which has two degrees of freedom of linear and rotational motions. Since differential wheeled mobile robots have non-linear cinematic characteristics, path planning and path control becomes very difficult to design from the viewpoints of optimality and stability. There exists inevitable path error between the current position of the robot and the desired path due to the imperfect tracking control of driving wheel velocities or environmental disturbances. This path deviation should be corrected by on-line adjustment of the desired linear and rotational velocities of the robot in the execution level called path-tracking control

Parameter estimation techniques for a rehabilitation hand exoskeleton

In this paper we study several techniques regarding the parameter estimation for a rehabilitation hand exoskeleton. Several solutions for the control system are proposed and discussed. The technical constraints determine the difficulty of the sensor placement on the exoskeleton area. In order to avoid these problems, a disturbance torque observer is used. Two control solutions are proposed. First, we discuss a conventional control with velocity and force observers. Then, the torque observer is used to compensate the compliance effects of the human hand and to control the actuation torque. Several simulation examples prove the proposed methods.

Hexapod robot locomotion over typical obstacles

In this paper the authors presents a series of simulations designed in Matlab in order to analyze the locomotion of a hexapod mobile robot over common obstacles in different applications. For the robot in question, the authors have developed the direct and inverse geometrical model for the robot leg and for the entire structure using Denavit - Hartenberg algorithm. The tests presented are a part of a complex simulation platform developed in Matlab that allows static stability analysis, full control of the robot, hardware and software leg motion control and locomotion analysis which is the main subject of this paper. There are also presented the most common types of obstacles that a legged robot can encounter during locomotion. In the end some simulations are included and discussed.

Experiments for Performance Evaluation of a Mobile Robot Trajectory Tracking

Generally, the path given by the 2D global path planner is a complex trajectory concerning straight lines, circular arcs, quick turning motion or lane change motion, but in the simplest case, the trajectory can be a polygonal shape. For the case of a differential wheeled mobile robot without spin motions, this paper presents and analyzes the real continuous evolution of the robot between two adjacent straight line of a polygonal rote, concerning different angles. For the same model of the robot, the control uses alternatively two different algorithms: the first one is a classical solution in path tracking control and the second one is an algorithm based on a smooth curve function.

Intelligent Live Environment Design with Assistive Robots for Vulnerable Persons

We present in this paper several ideas about the usability of the robotic arms and mobile robots as an assistive technology in a smart house where people with disabilities daily live. First, psychological and social aspects of smart home technology are presented and after that the modularity and standardization processes are discussed. Next we propose a smart house plan, equipped with a mobile robot which has a manipulator arm. This robotic system is used to help vulnerable persons, the handicapped men vehicle seat being equipped with a robotic arm which can manipulate objects by a hyper-redundant gripper. For the control of the processes in the smart house, we propose a hierarchical control system and for the mobile robot we use the artificial potential field method. Also, this paper points out the edutainment concept (EDUcation and enterTAINMENT) by robotics. Finally, some applications are presented.

Hybrid Control Strategies for Jumping Robots

The paper treats the control problem of the locomotion phases in a jumping cycle of a robot. The mechanical architecture of the leg with elastic lower segment (ATHLETE MODEL) is discussed. The dynamic model of the motion in stance phase is determined. The touch-down sequence, when the elastic foot hits the ground, is discussed and the control system is analyzed for two cases: actuator as passive damper system and actuator as semi-active damper system with ground-hook damper model. The transmissibility characteristics are analyzed. An active damper with ER fluids actuator and a skyhook viscosity controller is proposed to avoid the vibrations in the mechanical structure that can disturb the evolution of the robot. The control parameters are determined by using the circle criterion. The take-off sequence conditions in the stance phase are inferred by using the energy concept.

Hierachical sliding mode control for balancing athlete robot

The paper treats a class of human walking robots, the athlete robot (AR). The dynamic equations of this model are generated by Euler Lagrange method as a multi-input-multi-output under-actuated model. The balancing control on one leg in the stance phase is studied. The hierarchical sliding mode control algorithm is proposed. Numerical simulations show the method efficiency.

Dynamic Control for a Class of Continuum Robotic Arms

The paper deals with the control problem of a class of hyper-redundant robots constituted by a chain of continuum segments. The main parameter, the system state, is determined by the position and velocity generalised variables. The dynamic model is studied and the constraints of the state variables and nonlinear components are proved. The observability problems are solved by an approach derived from the Luenberger observer type extended for this class of non-linear distributed models. The inequality constraints on the gravitational components allow to introduce a decoupled control system. A PD boundary control algorithm is used in order to achieve a desired shape of the arm. The stability analysis and the resulting controllers are obtained using Liapunov techniques. The exponential stability of the (error-observer) system was proved. The constraints on the observer and controller gains are analysed. Experimental tests verify the effectiveness of the presented techniques.

Output Control of a Class of Hyper-redundant Robots

The paper studies the control problem of a class of hyper-redundant robots with uncertain components by using the output control. To avoid the complexity of distributed controllers, in this paper is proposed a lumped output controller. A weighted technique is used to generate a boundary output. A PD controller is proposed and an algorithm for determining the controller gains is discussed. Lyapunov techniques are used to prove the asymptotically stability of the control system. Numerical simulations and prove the efficiency of the method.