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What is automation?
An automatic controller is a self-acting or self-regulating mechanism that controls an object in
accordance with a desired behaviour. The object is for example an aircraft, set to follow a certain route.
The ball balancer laboratory rig below, the socalled cart-ball rig, illustrates automatic control. It
consists of a cart with an arc made of two parallel pipes on which a steel ball rolls. The cart moves on a
pair of tracks horizontally mounted on a heavy support. The control objective is to balance the ball on the top of the arc and at the same time place the cart in a desired position.
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Laboratory rig illustrating multivariable control. The rig is 1.5 meters long, equipped with a power supply and equipment for both analog and digital
control. |
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A student can push the cart left and right by hand, and balance the ball on top of the arc more or less,
at least after some training. It is not possible for any ordinary human being, though, to place the cart at a particular position also. An automatic control system can do that, nevertheless.
The cart position and ball angle from vertical are measured, and a horizontal force on the cart is the
control action. A wire pulls the cart, passing over a pulley in one end and a wire drum in the other end,
both attached to the support. The wire is driven by a motor and a controller applies the force according to a control strategy.
In order to make experiments easier, a simulator has been built to mimick the behaviour of the rig. It
contains a mathematical model, and a set of working parameters, such that the cart and ball can be set
in motion at the push of a button. When the system has come to rest, plots show the transient response of the cart position and velocity as well as the ball position and velocity.
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Matlab simulator of cart-ball rig. See the controller balance the ball (load animated gif). |
The controller is set to balance the ball at the top while placing the cart on the middle of the track. To
begin with the cart is at rest on the middle, and the ball rests on its left end-stop. Obviously, the cart must initially move left, in order to make the ball roll towards the top.
A degree in Automation can lead to a job in the automation industry. To get an idea of the typical
companies related to automation, students may visit the website of Dansk Automationsselskab, DAu
(the Danish Automation Society). It provides a list of members with contact addresses as well. A
degree can also lead to a job in a completely different business, since automation is interdisciplinary
and the feedback principle is a universal concept appearing in for instance, the human body, psychology, and economies.
There is another automation department in Denmark, the Department of Control Engineering at the
Aalborg University. Professor Jakob Stoustrup maintains a common web site, that can give an overview
of all automation activities in both universities. The Lund University in Sweden has a famous control
department, and Danish students can take courses there and get a credit transfer fairly easily. The
Industrial Engineering and Automation department, also in Lund, offers automation courses as well, perhaps with an angle towards applications rather than theory. Also Malmö Högskola (Malmö
University) offers practically oriented courses in automation.
 Courses in proceskontrol, Aalborg
Control in Denmark
Courses in Dept of Automatic Control, Lund
Courses in Dept Industrial Electrical Eng. and Automation, Lund
Courses at Malmö Högskola
Analysis of a Pendulum problem
Cart-Ball Simulator
Cart-Ball User's Guide
Company members of DAu
Contact: Ole Jannerup (homepage) <oej@oersted.dtu.dk >
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