Page 30 - The Mechatronics Handbook

electrical typewriters, and cameras. A further considerable simplification in the mechanics resulted from
introducing microcomputers in connection with decentralized electrical drives, as can be seen from elec-
tronic typewriters, sewing machines, multi-axis handling systems, and automatic gears.
The design of lightweight constructions leads to elastic systems which are weakly damped through the
material. An electronic damping through position, speed, or vibration sensors and electronic feedback
can be realized with the additional advantage of an adjustable damping through the algorithms. Examples
are elastic drive chains of vehicles with damping algorithms in the engine electronics, elastic robots,
hydraulic systems, far reaching cranes, and space constructions (with, for example, flywheels).
The addition of closed loop control for position, speed, or force not only results in a precise tracking
of reference variables, but also an approximate linear behavior, even though the mechanical systems show
nonlinear behavior. By omitting the constraint of linearization on the mechanical side, the effort for
construction and manufacturing may be reduced. Examples are simple mechanical pneumatic and electro-
mechanical actuators and flow valves with electronic control.
With the aid of freely programmable reference variable generation the adaptation of nonlinear mechan-
ical systems to the operator can be improved. This is already used for the driving pedal characteristics
within the engine electronics for automobiles, telemanipulation of vehicles and aircraft, in development
of hydraulic actuated excavators, and electric power steering.
With an increasing number of sensors, actuators, switches, and control units, the cable and electrical
connections increase such that reliability, cost, weight, and the required space are major concerns. Therefore,
the development of suitable bus systems, plug systems, and redundant and reconfigurable electronic systems
are challenges for the designer.

Improvement of Operating Properties
By applying active feedback control, precision is obtained not only through the high mechanical precision
of a passively feedforward controlled mechanical element, but by comparison of a programmed reference
variable and a measured control variable. Therefore, the mechanical precision in design and manufac-
turing may be reduced somewhat and more simple constructions for bearings or slideways can be used.
An important aspect is the compensation of a larger and time variant friction by adaptive friction
compensation [13,20]. Also, a larger friction on cost of backlash may be intended (such as gears with
pretension), because it is usually easier to compensate for friction than for backlash.
Model-based and adaptive control allow for a wide range of operation, compared to fixed control with
unsatisfactory performance (danger of instability or sluggish behavior). A combination of robust and
adaptive control allows a wide range of operation for flow-, force-, or speed-control, and for processes
like engines, vehicles, or aircraft. A better control performance allows the reference variables to move
closer to the constraints with an improvement in efficiencies and yields (e.g., higher temperatures,
pressures for combustion engines and turbines, compressors at stalling limits, higher tensions and higher
speed for paper machines and steel mills).

Addition of New Functions

Mechatronic systems allow functions to occur that could not be performed without digital electronics.
First, nonmeasurable quantities can be calculated on the basis of measured signals and influenced by
feedforward or feedback control. Examples are time-dependent variables such as slip for tyres, internal
tensities, temperatures, slip angle and ground speed for steering control of vehicles, or parameters like
damping, stiffness coefficients, and resistances. The adaptation of parameters such as damping and
stiffness for oscillating systems (based on measurements of displacements or accelerations) is another
example. Integrated supervision and fault diagnosis becomes more and more important with increasing
automatic functions, increasing complexity, and higher demands on reliability and safety. Then, the
triggering of redundant components, system reconfiguration, maintenance-on-request, and any kind of
teleservice make the system more “intelligent.” Table 2.2 summarizes some properties of mechatronic
systems compared to conventional electro-mechanical systems.

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