Mechatronics

Tasks of systems and machine dynamics

In system dynamics we are concerned with the prediction and analysis of the evolution of the system’s state. This state can be expressed in terms of temperature pressure, chemical concentrations, electrical currents, wear or damage etc.

Especially in machine and structural dynamics, we deal with the motion in terms of displacements, velocities and accelerations as well as with dynamic internal forces and moments in machine and structures. What we are interested in are e.g. the precision with which a robot can follow a given trajectory, the occurrence of unstable motion, amplitudes of vibration in a stationary state or the transient behaviour following to a disturbance of the system Some typical fields of applications can be found in

• automotive engineering (vehicle dynamics, vibration and noise),

• railway systems (high speed train ICE) and magnetic levitation systems (Transrapid),

• space vehicles and satellites,

• airplanes and helicopters,

• robotic systems,

• milling machines,

• printing machines,

• internal combustion engines,

• turbomachinery (steam turbines, water turbines, wind turbines, pumps and turbo compressors → rotor dynamics is a special field of machine dynamics,

• biomechanical systems: walking and mobility prosthetics,

 Mechatronics

Other names are used for this special class of problems, including controlled Mechatronics machines, smart machines, smart structures, and intelligent machines. The term mechatronics is mainly in use in Europe and Japan where mechatronic devices such as magnetic bearings or automated cameras have been pioneered.A large-scale application is the mag-lev train that has been developed in Japan

and Germany. Active magnetic bearings for small and large rotating machines such as pipeline pumps and machine tool spindles have been developed in Switzerland, France or Japan. In the USA a significant amount of research and development has been directed forward toward Micro-Electro-Mechanical Systems or MEMS. Other fields of interest are self-diagnosis of machines and structures using built-in diagnostic devices and computational intelligence as well as vibration and noise control.

The distinguishing feature of most of these systems compared to classical controlled machines has been the incorporation of sensing, actuation, and intelligence in producing and controlling motion in machines and structures. This means that we have to integrate control and intelligence into the mechanical design from the very beginning and not as an add-on after the machine is designed.

Dynamic Failures

While dynamic analysis in engineering is often used to create motions in physical systems, in many unwanted dynamic failures are to be avoided. Such failures include:

• large deflections,

• fatigue of materials from high or low amplitude vibrations,

• motion-induced fracture,

• dynamic instability, e.g. flutter or chatter,

• impact-induced local damage (e.g. delaminations of plies in carbon-fibre

reinforced plastics),

• motion-induced noise,

• instability about a steady motion, e.g. wheels on rails,

• thermal heating due to dynamic friction.

Avoidance of Dynamic Failure

• understand the dynamics before the design becomes a product, using

  simulation tools and/or measurements,

• choose materials with enhanced properties to resist fatigue, fracture or wear, or choose materials with  

   higher damping to minimize resonance,

• use passive damping,

• use active control,

• use internal diagnostics, sensors, limit switches , etc. to detect imminent

  failure and avoid catastrophe (Structural Health Monitoring (SHM)).

Of great importance is the knowledge of the sources and phenomena of unwanted vibrations. Vibrations may be induced by:

• oscillating and rotating machine parts with mass unbalance,

• periodic variations of the torque in internal combustion engines,

• interaction of mechanical machine parts with a fluid (turbulent wind

loads, self-excited vibrations , flutter),

• earthquakes (important in civil engineering but also in mechanical engineering in safety relevant areas like nuclear power plants),

• road roughness (road vehicles),