Michel Cotsaftis

Simulation of roll grinding system dynamics with rotor equations and speed control

Abstract A nonlinear dynamical model for paper machine roll grinding process is investigated through a group of delay differential equations with one constant time-delay. In this model, the time-delay effect is originated from shape error traces on the surface of the roll. The contact interaction of the roll and the grindstone is based on the wear theory, and the lateral deformations of the roll as a simply supported continuous beam element inside a rotational coordinate frame and the rotational rigid body vibration system are considered. The PD-controllers of the roll and the grindstone drives are also included. The numerical simulations for time-history responses provide a view of the stability of this grinding process for the design, analysis and verification of industrial roll grinding measurements in future.

Man-in-the-Loop Training Simulator for Hydraulic Elevating Platforms

Hydraulic elevating platforms are commonly used machinery in assembling outside covers to buildings, washing windows etc. Evacuation of people from high places as well as fire-fighting are also well known service areas of elevating platforms. A team of researchers, designers, and end-users has introduced a concept of a man-in-the-loop simulator to be used in operator training for time-critical and accurate boom maneuvers. The hardware consists of a boom platform mounted on a 3d Stewart platform. Virtual engineering software is used to visualize the working environment on wall screens while a real-time simulation model transforms large boom movements to produce restricted motion in the Stewart mechanism.

Dynamical and thermal modelling of creep and relaxation for force and weight sensors

We present in this article analytic formulations of creep and relaxation processes, including thermal variation, for force and weight mechatronic sensors. We found that these phenomena can be modelled by a two timescales process for the dynamical behaviour of creep and relaxation, and that under a quasi static assumption of the temperature evolution thermal variation can be given, under usual range of temperature, by a polynomial representation of low order.

Performance Analysis of Drive-Line Steering Methods in Excavator-Mounted Sheet-Piling Systems

Sheet-piling processes pose the problem of guiding the pile to follow a fixed trajectory in order to drive it correctly into the ground. Since the complete system consists of the supporting excavator boom with hydraulic actuators, the gripper, and the vibratory unit, the large number of system variables implies the use of servo control to allow a human operator to handle the operation. An exact inverse kinematic transformation from Cartesian workspace to boom joint space variables allows the pile penetration to be guided, keeping the valve input of the main boom actuator as the free parameter, while the remaining actuators are governed automatically by the control computer. The penetration record of the pile differs based on whether a constant valve input is used in semiautomatic steering mode or, alternatively, the desired penetration speed is governing the valve input in a feedback loop in full-automatic steering mode. A numerical model representing an actual industrial system has been developed. Variable results from computer simulations have led the manufacturer to realize the steering system. It has been verified in real piling tests that the steering system may be tuned to be stable and fast enough for practical working conditions. In particular, the performance of trajectory control in terms of tracking error is much better than in the conventional manual steering method, as expected.

Trajectory Control Performance Analysis of Excavator-Based Sheet-Piler-System

Sheet-piling process poses the problem of prescribing the pile a fixed trajectory in order to drive it correctly into the ground. When representing the complete system of the supporting boom with hydraulic actuators, the gripper and the vibratory unit, the large number of system variables implies the use of assisted control to allow a human operator to handle the operation. Based on exact kinematic transformation from boom state space variables to cartesian workspace ones, a simple control procedure linking boom variables reduces inputs to only one which determines the advance of the pile in the ground. A numerical model representing an actual industrial system has been developed. It is verified that the resulting trajectory is very stable and is leading to small tracking error in following a prescribed trajectory when compared to manual performance in similar conditions.

Soft high precision contact positioning control

The problem of approaching with high precision contact two generally actuated objects or work-pieces in industrial environment is discussed in a large parameter range. It is first noticed that main three actuation systems, electrical, pneumatic and hydraulic, obey the same type of equations which are coupled to object dynamics including its specific material reaction. For complete safety, especially for avoiding excitation of long lasting and potentially damaging vibrations, a controller is researched which guarantees that at contact the two object are at full rest with respect to each other in the sense that both relative velocity and acceleration are strictly zero. This is not always the case with usual position and force controls. Present controller is an explicit family of extended PDA-type one including on top a new part the role of which is to exactly fulfill contact conditions. It is shown that minimum time control is not possible and that minimum energy control is not easily realizable, owing to natural system constraints. A workable control, allowing to achieve extremely high precision in micron range, is analytically displayed.

Integrated control for high accuracy complex system

For high performance outputs, industrial or technical systems development rests upon better performing components with on top a controller acting with its specific features. As ultimately a larger frequency domain than presently covered by actuators is used, robustification of controllers is required as with modern ones improved over classical PID. They usually provide more efficient splitting of frequency band into lower range for power input with high gain for performance, and higher range with small gain for robustness. However, obtained stability is only simple, and the limit is often reached for moderate performance even with high quality components for partly known and/or intrinsically too noisy systems, where performance level and power requirement cannot be simultaneously met. This effect is the larger as the system size becomes smaller, and its structure more complex as in modern micro-systems. The problem has to be reassessed, and another controller giving asymptotic stability is proposed, and further improvement by distributing the controllers location in an optimum design view of the system is analyzed on a general nonlinear split n-dimensional dynamical system.

Dynamics and Monitoring of Vibratory Piling Process

The foundations of buildings in urban environments are very often piled ones. During earth moving works the sides of digging area have to be supported by sheet pile walls to maintain constant earth pressure conditions against existing foundations. The piles and sheet piles are very often driven by vibratory methods, in which case the ground vibration is a risk for neighboring old buildings. The purpose of the present research work is to find a new, theoretically well established way to use vibratory pile drivers environmentally friendly especially in urban environments. Closely related to this a new electro-hydraulic circuit has been introduced by Unisto company for on-line adjusting of the phase angle between primary and secondary shafts of eccentric masses in the vibratory unit. Furthermore, the control of this angle will be subjected to continuous monitoring from the vibration level of the critical structure to be protected. The control of shafts phase angle is based on separate drive technology, in which the position difference is governed by electrically controlled orifices. Vibration control principle is based on the requirement to stay below required vibration bounds in the working environment. The system is equipped with a vibration sensing box to be fixed on to the protected structure, from which the vibration level information is transmitted to the control box of vibratory unit. The described system is investigated both theoretically and numerically. The theoretical part of the research includes the derivation of complete system equations. In the numerical part of the work the system is coded and simulated by computer to get required information for system modifications and dimensioning. The main objective of these research steps is to evaluate the operation of phase angle adjusting system in order to balance the control of environmental vibrations and machine performance.

Dynamics of training simulator for mobile elevating platforms

This chapter discusses a training simulator concept that has been developed for operator training of hydraulic elevating platforms. Intervention in high place such as buildings requires hydraulic elevating platforms commonly used for assembling outside covers, washing windows, as well as inspection and safety for repairs, rescuing persons and fire fighting. As these platforms are aimed at providing a complex service, their operation, even when simplified by adequate design, requires a sophisticated action, which has to be learned by operator using a concept of a man-in- the-loop simulator. The simulator consists of the elevator platform mounted on a classical Stewart platform. Amplitudes of platform motion are reduced at actuator control level and smaller movements than in the real boom system are produced. As a consequence for validation of the simulator, a strong limitation is coming from the needs of a simulation model satisfying contradictory properties of accuracy and real time computation, which is transforming large boom movements to produce restricted motion in the Stewart mechanism.

Eigenfrequencies Invariance Property in One-Link Robotic Arm

In the study of eignefrequencies of robotic arms versus load, straightforward invariance property is singled out under a preload condition. We show that compliance does not affect this effect. This property opens the way to new robust and finite dimensional controllers.