Agriculture Reference
In-Depth Information
use of vision in agricultural automation. Vision sensing is especially used to identify
and locate items of interest, be they agricultural products or objects in the envi-
ronment. Vision is also commonly used to find defects and make other qualitative
evaluations.
Satellite navigation systems, such as Global Positioning System, GLONASS,
GALILEO, and COMPASS allow more location and navigation sensors to be added
to agricultural automation systems. Advances in such areas as microelectromechani-
cal systems, Coriolis sensors, and nanotechnology are also providing new sensing
methodologies for the future.
Sensor static and dynamic performance is often influenced by sensor cost.
Agricultural automation sensors are often selected from those of moderate cost.
Agricultural automation applications usually cannot afford the sensors used in high-
end systems, such as those typically used in aerospace applications. However, more
costly sensors can be justified for agricultural applications than for many consumer
goods. Unfortunately, the relatively low manufacturing volumes of agricultural auto-
mation systems do not allow the sensor research and development or the manufactur-
ing economies of scale of many other industries.
1.4 CONTROLLERS
After the agricultural automation systems have gathered data through the sensors,
a decision about what to do has to be made. This is the realm of what is here being
termed the controller. It must integrate all the information received from the various
sensors and decide what the appropriate action should be.
Controllers can be classified by the number of states of the output of the control-
ler. Generally, the more states of the output, the more complicated and costly the
controller will be. They will be initially classified here into on-off, discrete-output,
and continuous controller categories.
On-off control is the simplest control. Consider, for example, a simple heating
system. If the temperature of concern is below a certain setpoint, the heating system
will be on. If the temperature is below that value, the heating system will be off.
Such systems can function with very simple sensors and controllers. For example,
a simple temperature-activated switch can perform both sensor and controller func-
tions simultaneously.
However, if there are many quantities to be sensed and/or many system outputs to
be controlled, even systems with on-off control get more complicated. Techniques of
sequential control may be used in relay controls or programmable logic controllers.
Modern controllers of this type use a computer to check the states of all the inputs,
to make a decision based on a program, and then to issue commands to the actuators.
The controller may be designed with more sophisticated techniques, such as the use
of truth tables or state transition diagrams. Such systems are very popular in indus-
trial applications and seem to be increasing in agricultural applications.
Most of the current agricultural automation applications discussed in this topic,
however, are of a different type. One, or a small number, of outputs are controlled.
But they are not just on-off. The next level of sophistication after on-off is the
three-position controller version of the discrete-output controller. Simple examples
