Experimental studies on damping by parametric excitation using electromagnets

2012 ◽  
Vol 226 (8) ◽  
pp. 2015-2027 ◽  
Author(s):  
F Dohnal
Keyword(s):  
Parametric Excitation ◽  
Vibration Suppression ◽  
Experimental Studies ◽  
Mechanical Systems ◽  
Variable Stiffness ◽  
Excitation Amplitude ◽  
Open Loop ◽  
Basic Step ◽  
Mass System ◽  
Loop Control

Transient vibrations in mechanical systems are a common problem in engineering. Several theoretical studies have shown analytically and numerically that a vibrating system can be stabilised or its vibrations can be reduced when excited close to a specific parametric combination resonance frequency. At this operation, the transient vibrations are effectively damped by parametric excitation. The basic step in exploiting this method is its experimental implementation in mechanical systems. In this review, recent experiments are discussed for a simple chain mass system, a continuous cantilever and a flexible rotor system. The parametric excitation is realised by electromagnetic variable-stiffness actuators driven by a periodic open-loop control. It is demonstrated experimentally that a parametrically excited structure can exhibit enhanced damping properties. A certain level of the excitation amplitude has to be exceeded to achieve the damping effect in which the existing damping in the system is artificially amplified. Upon exceeding this value, the additional artificial damping provided to the system is significant and most effective for vibration suppression of the lower vibration modes.

Experimental Results on Parametric Excitation Damping of an Axially Loaded Cantilever Beam

2009 ◽  
Author(s):  
Horst Ecker ◽  
Thomas Pumho¨ssel
Keyword(s):  
Cantilever Beam ◽  
Parametric Excitation ◽  
Vibration Suppression ◽  
Excitation Frequency ◽  
Open Loop ◽  
Piezo Actuator ◽  
Combination Frequency ◽  
Bending Vibrations ◽  
Periodic Force ◽  
Parametrically Excited

In various fields of engineering, e.g. aerospace applications, robotics or the bladings of turbomachinery, slender beam-like structures are in use and subject to free bending vibrations. Since such vibrations often are not wanted because they may degrade the performance or function of the structure, it is important to have a suitable means of vibration suppression available. In this experimental study we investigate a slender cantilever beam loaded with a controlled force at its tip. The force is always oriented towards the clamping point of the beam and generated by a piezo-actuator. Force control is based on an open-loop control without feedback from the structure. To enhance vibration suppression we take advantage of the additional damping observed when a periodic force modulation at a certain frequency is applied. From several theoretical studies it is known that parametrically excited systems show increased stability, and therefore enhanced damping properties, when the parametric excitation frequency is chosen near a certain combination frequency. Due to the almost axially applied force the cantilever beam system becomes a parametrically excited system and the effect mentioned can be observed. Numerous measurement runs have been carried out and vibration suppression as a function of the excitation frequency, the excitation amplitude and the beam initial deflection has been investigated. The results are in very good agreement with theoretical predictions and for the first time the numerical and analytical results obtained earlier are confirmed by experimental work.

Rapid Swing-Free Transport of Nonlinear Payloads Using Dynamic Programming

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Daniel Zameroski ◽  
Gregory Starr ◽  
John Wood ◽  
Ron Lumia
Keyword(s):  
Dynamic Programming ◽  
Vibration Suppression ◽  
Robot Manipulator ◽  
Open Loop ◽  
Discrete Time System ◽  
Loop Control ◽  
Free Transport ◽  
Freely Suspended ◽  
Dynamic Description ◽  
Loop Motion

Residual vibration suppression in freely suspended payload transports has been the focus of extensive work in the past. Many methods have been used to address this problem, including both open-loop motion planning and closed-loop control techniques. However, to be effective, most of these methods require linearization of the system and, in turn, have been restricted in their maneuver speeds. The inherent nonlinearity of suspended payload systems suggests the need for a more rigorous method, where the complete dynamic description can be retained throughout the optimization. Dynamic programming (DP) is such a method. This paper will outline the development of the DP algorithm for a discrete time system as well as its application to the rapid transport of a doubly suspended payload, a nonlinear system. The system consists of a long slender payload, suspended by a cable at each end. The two cables are each held by an independent robot manipulator. We will show that DP is effective at reducing residual oscillations for nonlinear systems, as demonstrated by both simulations and experimental validation. Residual oscillations were suppressed to less than 5% of their original magnitudes.

Experimental Studies of Process Control

1985 ◽  
Vol 29 (4) ◽  
pp. 330-332
Author(s):  
Neville Moray ◽  
Ira Rotenberg
Keyword(s):  
Process Control ◽  
Common Factor ◽  
Experimental Studies ◽  
Open Loop ◽  
Transition Matrices ◽  
Display Design ◽  
Loop Control ◽  
Generic Problem ◽  
Changing Patterns ◽  
The 1960S

In the 1960s Crossman performed some classic laboratory studies of process control, requiring the operator to control the temperature of a container of fluid against fluctuations caused by the environment. This led to a model of the novice controller as a damped second order controller, who changed to open loop control with practice. We have recently repeated and extended this work with a simulated process control system made up of 4 Crossman tasks coupled together, and making the task more complex by requiring temperature, fluid level, and flow rate all to be controlled. Two aspects of the research will be reported. The first deals with the behavioural data. Changing patterns of skill are revealed as changes in the transition matrices. Weaknesses in display design, and cognitive lockup during fault management are revealed by patterns of eye movements. The second problem is a generic problem in the analysis of complex user-machine system. What kind of summary statistics are appropriate for describing operator skill? The problem here is that the desired performance is specified as a goal, not as behaviour. Since there are many behaviour patterns any of which can satisfy the goal, averaging is not appropriate, since the result frequently approximates noise. But to record merely a catalogue of individual behaviours is clumsy, and also fails to capture the fact that something is in fact present as a common factor in all performance - namely satisfactory achievement of the goal. The problem is how to represent the core of behaviour. Various methods will be described for overcoming this problem of representing complex dynamic behaviour, and their virtues and drawbacks discussed. The overall aim is to suggest improved ways to investigate process control and supervisory control.

Simple Dynamics and Open-Loop Control for Horizontal Boom Motion of Rotary Cranes

2014 ◽  
Author(s):  
Naoki Uchiyama ◽  
Shigenori Sano ◽  
Huimin Ouyang
Keyword(s):  
Simple Model ◽  
Vibration Suppression ◽  
Open Loop ◽  
Algebraic Equations ◽  
Open Loop Control ◽  
Residual Vibration ◽  
Loop Control ◽  
Rotary Crane ◽  
Nonlinear Force ◽  
Residual Vibration Suppression

This paper presents a simple model of rotary crane dynamics that includes only significant nonlinear force terms. This simple model allows to derive analytical solutions of the differential equations of the model. Thus, a simple trajectory that considers residual vibration suppression without sensing it, using only horizontal boom motion, can be generated by solving algebraic equations numerically. The effectiveness of the proposed method is demonstrated by numerical simulations and experimental results.

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