Erno Keskinen

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.

Dynamic compression testing of particle-reinforced polymer roll cover materials

Abstract Two polymer composite roll cover materials were studied using dynamic compression tests. The main focus was determination of viscoelastic properties of the materials and development of mathematical models to describe the behavior of these materials in the contact area between two rolls. The compression tests were conducted using short rise time pulses with different durations in servohydraulic materials testing machines. In the modeling, combinations of standard elastic and viscoelastic elements were used together with the Boltzmann superposition principle. A simple spring-dashpot model was found to fit sufficiently to the experimental data with relaxation (retardation) times ranging from a few milliseconds in transient loading tests to tens of hours in static compression tests

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.

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.

Hydrodynamic Added Mass and Damping of the Kaplan Turbine

Kaplan turbine runner rotates in water flow inside an enclosed discharge ring. The vibratory runner motion in the fluid flow induces pressure forces onto the wet runner surfaces with inertia effects conveniently described by the so-called hydrodynamic added mass and damping. These inertia effects influence the wet natural frequencies and the amplitudes. The role of the hydrodynamic added mass and damping in the Kaplan turbine shaft rotor dynamics has not been sufficiently well understood. This paper focuses on comprehensive understanding of these phenomena across the Kaplan design range. The results are based on a method derived from Theodorsen’s unsteady thin airfoil theory and on the Finite Element Method (FEM). The former method includes the water flow, the runner rotation and the circulatory effects, which makes it possible to calculate the added damping and evaluate the accuracy of FEM. The most critical vibration modes and shaft line configurations have been identified with inherent weaknesses in typical shaft line models. The added damping has been quantified. The numerical results have been compared to the experimental results.Copyright

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.

Multibody Analysis of Axially Elastic Rod Chains

Axially elastic rods are basic machine elements in hydraulic hammers, pilers and percussive drills [1]. The problem to analyze the motion history of such mechanisms is a very complex one, because the rods are simultaneously in large amplitude axial motion superimposed with a small amplitude elastic wave motion. The wave motion experiences division to reflected and transmitted components at each rod-rod interface depending on the current boundary stiffness [2]. The wave motion in each rod can be computed by finite elements or alternatively in space of semidefinite eigenfunctions. The feasibility of these methods in solving wave propagation problems in multi-rod systems with nonlinearly behaving rod-rod interfaces has been investigated and evaluated. The object of the experimental case study is a classical Hopkinson split bar apparatus [3] used in experimental analysis of material response to shock pulses. Another example representing a pile hammering system [4] evaluates the computational performance of the proposed approaches in long-term simulation of a complete work process.

Design of Fuzzy Logic-Based Controller in Roll Grinding System With Double Regenerative Chatter

This paper proposes application of fuzzy logic control (FLC) to do vibration control for the roll-grinding machine system with double regenerative chatter. In this paper, a multiple-degree-of-freedom (MDOF) model is developed to represent the dynamics behaviors of this kind of system. The dynamic system has double delays and lumped cutting parameters which make vibration control challenging. Numerical simulation shows that FLC can dramatically reduce the vibration levels compared to a convention control method.Copyright

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.

Multi-Body Modeling of Paper Calendering Unit by Contact Dynamics Formulation

A multi-body contact dynamics formulation is introduced to model the dynamic motion of roll mechanisms typical for paper manufacturing systems. Contacts between rolls manipulating the paper web are modeled as physical contact line loads in normal pressing and tangential traction directions. In the case study the new loading mechanism of a laboratory calender has been dynamically tested by means of system level simulations.