4 Sensor, signal, operator and control elements
The sensor, signal, operator and control elements are described in this chapter.
These elements allow control of the system (as opposed to sensors for output
purposes, see Reference Manual). A desired time-dependent motion or load
can be defined with a function signal element. Sensor, external input and
function signals can be manipulated with operators and PID controllers.
The output signals of all sensor, operator and control elements can be used as:
? input signals for operators and controllers,
? input for actuators that apply forces or torques to bodies,
? input for switches that define state conditions,
? input for external output signals that define interaction with external
programs.
4.1 Sensors
Sensors can be used to extract the quantities of multi-body systems and airbag
chambers. The output value of a sensor can be used as input for signals, operators,
controllers and actuators. The types of sensors available are:
? airbag sensors.
? belt sensors.
? body sensors.
? joint sensors.
? surface distance sensors.
? restraint sensors.
? contact sensors.
? switch sensors.
? node distance sensors.
Explicit methods are conditionally stable and therefore put limitations on
selection which time step can be used. Due to the fine spatial discretization often required,
a much smaller time step is needed for finite element models than for
multi-body models. To increase the efficiency of the entire analysis, the finite
element analysis is sub-cycled with respect to the multi-body analysis using a
different constant time step for each finite element model. If contacts between
different finite element models are specified, the time step is identical for all
the finite element models that are in contact. MADYMO automatically selects
the smallest time step used in any of the finite element models defined.
In order to be able to model parts of belts with membrane or truss elements,
a node can be tied to a belt segment (See "Belt model" on page 169). All current
belt model options can be used, including retractors, pretensioners and
load limiters, so the finite element belt model can slide over dummy model
surfaces.
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