Ambrus Zelei

• Doctor of Engineering
• Budapest University of Technology and Economics

Stability problems of robotic systems arise sometimes suddenly, seemingly for no reason. The digital time sampling is often the main cause of these instabilities. Discrete models, which are capable of the prediction of stability, are available for low-degree-of-freedom template models of linear position and force control. However, for the inverse d...

To analyse walking, running or hopping motions, models with high degrees of freedom are usually used. However simple reductionist models are advantageous within certain limits. In a simple manner, the hopping motion is generally modelled by a spring-mass system, resulting in piecewise smooth dynamics with marginally stable periodic solutions. For a...

This study examines the management of noise, vibration, and harshness (NVH) in electric vehicle (EV) powertrains, considering the challenges of the automotive industry’s transition to electric drivetrains. The growing popularity of electric vehicles brings new NVH challenges as the lack of internal combustion engine noise makes drivetrain noise mor...

The radiated noise reduction of vehicular power transmission systems is one of the most actively researched areas. Noise not only impacts the comfort and safety of the driver and passengers but also regulated by the legislators. The simulation-based prediction of radiated noise of gear-drives is a rapidly evolving area and combines gear meshing mod...

This study focuses on the optimization dynamics of racing go-karts, which is heavily influenced by the frame's stiffness. Lacking suspensions and differentials, go-karts rely on the frame stiffness for wheel balancing and skid prevention by lifting the inner rear wheel during turns. Utilizing a rigid-flexible model in MSC Software ADAMS View, valid...

Annak ellenére, hogy a futás és szökdelés tömeg-rugó modellje (SLIP – spring-loaded inverted pendulum) nagyon széles körben alkalmazott, nem találtunk teljes térképet a stabil mozgások dimenziótlan paramétertartományaira és a vonzási tartományokra. A Buckingham-féle Pi-tétel segítségével minimálisan szükséges paraméterhalmazt vezetünk be. Feltárjuk...

The spring-loaded inverted pendulum is a widely used model of legged locomotion. However, a complete map of the dimensionless parameter regions that correspond to the stable periodic solutions cannot be found in the literature. In this work, the three-dimensional space of two dimensionless physical parameters and the dimensionless total mechanical...

Postural sway is a result of a complex action–reaction feedback mechanism generated by the interplay between the environment, the sensory perception, the neural system and the musculation. Postural oscillations are complex, possibly even chaotic. Therefore fitting deterministic models on measured time signals is ambiguous. Here we analyse the respo...

Spatial pose estimation devices for mobile and cable-suspended robots have been rapidly developed. The HTC Vive sensor, which operates with swept laser beams, has aroused many researchers’ interest. We present experiments with a double pendulum robot equipped with the HTC Vive Tracker. A linear feedback controller ensured the tracking of pre-define...

The tracking control of underactuated systems is a challenging problem due to the structural differences compared to fully actuated systems. Contrarily to fully actuated systems, resolving the inverse kinematics problem of underactuated systems is not possible independently from the dynamic equations. Instead, the inverse dynamics must be addressed...

The relation between balancing performance and reaction time is investigated for human subjects balancing on rolling balance board of adjustable physical parameters: adjustable rolling radius R and adjustable board elevation h . A well-defined measure of balancing performance is whether a subject can or cannot balance on balance board with a given...

For both non-redundant and redundant systems, the inverse kinematics (IK) calculation is a fundamental step in the control algorithm of fully actuated serial manipulators. The tool-center-point (TCP) position is given and the joint coordinates are determined by the IK. Depending on the task, robotic manipulators can be kinematically redundant. That...

Postural sway is a result of a complex action-reaction feedback mechanism generated by the interplay between the environment, the sensory perception, the neural system and the musculation. Postural oscillations are complex, possibly even chaotic. Therefore fitting deterministic models on measured time signals is ambiguous. Here we analyse the respo...

The reaction time, which is also referred as reflex delay in the literature, is an important factor in human balancing, since reaction time highly affects the ability of self stabilization. Increased reaction time delay may cause dangerous fall-over accidents related to elderly people. Reaction time depends on age, health, everyday activities, the...

Human and robotic legged locomotion can be described with complex multi-degree-of-freedom dynamic models, whose bifurcation or parameter analysis may explain some features of typical patterns during motion. In this paper, we focus on the effect of kinematic parameters and foot placement techniques on the ground-foot impact intensity. The work is ba...

The dynamic analysis of legged locomotion typically involves issues related to multibody dynamics, underactuation, motion planning and stability. In addition to biomechanics of humans and animals, the dynamic analysis of legged locomotion is also an important issue in the control development of pedal robots. For these robots, stable internal dynami...

Our research aims the study of balancing on a rolling balance board with respect to dynamic properties such as stability and stabilizability. The goal is to identify the parameter regions where human subjects are able to keep themselves stable in the upright position for at least 60 s. The radius of the balance board and the height of the foot plat...

Contradictory demands are present in the dynamic modeling and analysis of legged locomotion: on the one hand, the high degrees-of-freedom (DoF) descriptive models are geometrically accurate, but the analysis of self-stability and motion pattern generation is extremely challenging; on the other hand, low DoF models of locomotion are thoroughly analy...

Biomechanical models of different complexity are used to understand the dynamics of human running. Low degrees-of-freedom models are appropriate for the prediction of the effect of certain parameter changes. We present a minimally complex biomechanical model which characterizes the effects of foot strike pattern and shank angle on the ground-foot i...

A two-degree-of-freedom mechanical model was developed to analyze human balancing on rolling balance board in the frontal plane. The human nervous system is modeled as a proportionalderivative controller with constant feedback delay. The radius R of the wheels and the board distance h measured from the center of the wheel are adjustable parameters....

Human balancing on rolling balance board in the frontal plane is analyzed using a two DoF mechanical model, where the human body is modeled by a four-bar linkage mechanism and the geometry of the balance board can be adjusted. Human nervous system is assumed to employ a proportional-derivative controller with constant feedback delay identical to th...

The dynamic analysis of legged locomotion is challenging because of many reasons, such as the possibly high degrees of freedom of the model, the alternating topology in certain phases of walking or running, the presence of under-actuation and over-actuation, the geometric nonlinearities and ground-foot impact induced non-smoothness. Control issues...

The model-based motion control of underactuated, multiple degree-of-freedom, complex multibody systems is in focus. Underactuated mechanical systems possess less number of independent control inputs than degrees-of-freedom. The main difficulty in their control is caused by the dynamics of the uncontrolled part of the system. The complexity of multi...

Human balancing on a balance board is modelled as a delayed proportional-derivative control mechanism with unknown feedback delay. The mechanical model implies that there exists a critical delay, for which no control gain parameters can stabilize the system. This theoretical critical delay is determined by numerical analysis for different geometrie...

Model-based control methods such as inverse dynamics control and computed torque control encounter difficulties if actuator saturation occurs. However, saturation is a common phenomenon in robotics leading to significant nonlinearity in system behavior. In this study, the saturation of the actuator torques is considered as a temporary reduction of...

The biomechanical analysis of human running is a complex problem, because of the large number of parameters and degrees of freedom. However, simplified models can be constructed, which are usually characterized by some fundamental parameters, like step length, foot strike pattern and cadence. The bouncing ball model of human running is analysed the...

The domestic robot platform Acroboter exploits a novel concept of ceiling based locomotion. The robot platform is designed to perform pick and place tasks as well as carry other service robots with lower mobility. The crane-like Acroboter platform extends the workspace of these robots to the whole cubic volume of the indoor environment by utilizing...

Flutter instability is a typical aerodynamic vibration phenomenon of slender elastic bridges. The sensitivity for flutter can be predicted by determining the so-called nutter derivatives from the small-scale model of the bridge. This work investigates an elastic supported two d.o.f. bridge section model which can move vertically and rotate around a...

Nature is a storehouse of great ideas, which are mostly so well planned, that engineers can apply them directly via examining, understanding and imitating the natural working principles. Snakes and worms can be found in almost every region of our planet. Their success is mainly based on the simple construction of their body and their robust locomot...

The domestic robot platform ACROBOTER exploits a novel concept of ceiling based locomotion. A climber unit moves on the almost obstacle free ceiling, while carries a swinging unit with a system of suspending and orienting cables. The objective of the robot is the fine positioning of the swinging unit that accomplishes path following or pick and pla...

In this paper we investigated the dynamics of a thin, flat plate placed in potential planar flow and attached by springs to the wall. Furthermore, the centre of gravity of the plate was assumed to move only perpendicular to the direction of the flow. Thus, a two-degree-of-freedom oscillatory system was analysed, whose natural frequencies depend on...

Computed torque control (CTC) method is an efficient technique for trajectory tracking control of robot manipulators. As a model-based control, CTC needs the inverse dynamics calculation of the dynamical system. A special group of these systems is formed by the underactuated ones, in which the number of independent control inputs is lower than the...

The paper investigates the motion planning of a suspended service robot platform equipped with ducted fan actuators. The platform consists of an RRT robot and a cable suspended swinging actuator that form a subsequent parallel kinematic chain and it is equipped with ducted fan actuators. In spite of the complementary ducted fan actuators, the syste...

This paper presents the conceptual design and the dynamics modeling aspects of a pendulum-like under–actuated service robot platform ACROBOTER. The robot is designed to operate in indoor environments and perform pick and place tasks as well as carry other service robots with lower mobility. The ACROBOTER platform extends the workspace of these robo...

The paper presents the motion control of the ceiling based service robot platform ACROBOTER that contains two main subsystems. The climbing unit is a serial robot, which realizes planar motion in the plane of the ceiling. The swinging unit is hoisted by the climbing unit and it is actuated by windable cables and ducted fans. The two subsystems form...

This paper aims to generalize the computed torque control method for underactuated systems which are modeled by a non-minimum set of generalized coordinates subjected to geometric constraints. The control task of the underactuated robot is defined in the form of servo constraint equations that have the same number as the number of independent contr...

The recent work presents the motion control of a pendulum like under—actuated service robot AC ROBOT ER. This robot is designed to be applied in indoor environments, where it can perform pick and place tasks autonomously and/or with close cooperation with humans. It can also serve as a platform that carries other service robots with lower mobility....

The paper presents the dynamic analysis of a crane-like manipulator system equipped with complementary cables and ducted fan actuators. The investigated under-actuated mechanical system is described by a system of differential-algebraic equations. The position/orientation control problem is investigated with respect to the trajectory generation and...

In the present study, we investigate the possibility of stabilizing a floating body that is unstable without parametric excitation. We prescribe a non–stationary geometric constraint, that is, the centre of gravity is moved periodically in vertical direction. This periodic movement causes the parametric excitation described by a non–autonomous diff...

We investigate the motion of swinging payloads connected to a cable of moving suspension point by extending the methods of robotics. In general, the suspension point is moved by a crane, but in specified applications it can also be moved by a robot. In this case the swinging load has to be capable to follow spatial target trajectories and to keep d...

In this paper we propose a concept of a modular robot that can mainly be used for testing control algorithms in research work and in education. In our research work the main purpose is the experimental testing of com-puted torque control algorithms of underactuated dy-namical systems, which are modeled by non-minimum set of descriptor coordinates....