Figure 13.1 The car painting equipment
receive paint flows from outside the work cell and supply paint flows to the
mixture tank through pipes.
Every tank has input and output pumps that generate the paint flows. The
mixture tank outputs mixed paint through a spray pump. A drain pump is
used to empty the mixture tank when necessary. The colour and mixture
tanks are equipped with sensors that measure the current paint level.
The SCADA system is made up of a network of distributed software con-
trollers that regulate the paint level of the colour tanks, the paint tonality
of the mixture tank, and the output flow of the spray pump under the
supervision of a responsible technician.
Programmable logic controllers
Colour tank controllers are software applications that emulate classical
programmable logic controllers (PLCs) and offer two functionalities:
They open and close the output pump in order to guarantee a given output
They open and close the input pump in order to guarantee that the tank
gets neither full nor empty. For this purpose the controller reads sensor
measures that indicate the current paint level in the tank.
The mixture tank controller is a PLC that offers two additional function-
It communicates with the tank controllers in order to pump the desired
flow of paint into the mixture tank.
It determines the percentage of paint volume for each fundamental colour
in order to get the desired colour mixture. When a new tonality is required
and the mixture tank is not empty, the controller should take into
account the current volume and tonality of paint in the mixture tank.