Page 447 - Mechanical Engineers' Handbook (Volume 2)

438 Basic Control Systems Design

can be programmed through user-friendly graphical interfaces. Examples include the Galil
motion controllers and the add-on modules for Labview and MATLAB.

12.3 Embedded Control Systems and Hardware-in-the Loop Testing
An embedded control system is a microprocessor and sensor suite designed to be an integral
part of a product. The aerospace and automotive industries have used embedded controllers
for some time, but the decreased cost of components now makes embedded controllers
feasible for more consumer and biomedical applications.
For example, embedded controllers can greatly increase the performance of orthopedic
devices. One model of an artificial leg now uses sensors to measure in real time the walking
speed, the knee joint angle, and the loading due to the foot and ankle. These measurements
are used by the controller to adjust the hydraulic resistance of a piston to produce a stable,
natural, and efficient gait. The controller algorithms are adaptive in that they can be tuned
to an individual’s characteristics and their settings changed to accommodate different phys-
ical activities.
Engines incorporate embedded controllers to improve efficiency. Embedded controllers
in new active suspensions use actuators to improve on the performance of traditional pas-
sive systems consisting only of springs and dampers. One design phase of such systems is
hardware-in-the-loop testing, in which the controlled object (the engine or vehicle suspen-
sion) is replaced with a real-time simulation of its behavior. This enables the embedded
system hardware and software to be tested faster and less expensively than with the physical
prototype and perhaps even before the prototype is available.
Simulink , which is built on top of MATLAB and requires MATLAB to run, is often
used to create the simulation model for hardware-in-the-loop testing. Some of the toolboxes
available for MATLAB, such as the control systems toolbox, the signal-processing toolbox,
and the DSP and fixed-point blocksets, are also useful for such applications.

13 SOFTWARE SUPPORT FOR CONTROL SYSTEM DESIGN
Software packages are available for graphical control system design methods and control
system simulation. These greatly reduce the tedious manual computation, plotting, and pro-
gramming formerly required for control system design and simulation.

13.1 Software for Graphical Design Methods
Several software packages are available to support graphical control system design methods.
The most popular of these is MATLAB, which has extensive capabilities for generation and
interactive analysis of root-locus plots and frequency response plots. Some of these capa-
bilities are discussed in Refs. 1 and 4.

13.2 Software for Control Systems Simulation
It is difficult to obtain closed-form expressions for system response when the model contains
dead time or nonlinear elements that represent realistic control system behavior. Dead time
(also called transport delay), rate limiters, and actuator saturation are effects that often occur
in real control systems, and simulation is often the only way to analyze their response.
Several software packages are available to support system simulation. One of the most pop-
ular is Simulink.