During the spring term 2006 a student project
was carried out. The aim of the project was to
position a shuttle on a rod less pneumatic cylinder using ON/OFF-valves. This type of
valves requires careful regulation that is
more complicated than conventional regulation using more expensive servo valves.
System overview
Group members at the test stand
From left: Carl-Johan Thell, Ola Sylvan, Mirsad Ferhatovic’
Results
1000
900
800
700
600
position[mm]
The system consists of a pneumatic cylinder and
valves that is used for developing automation controls. The cylinder has two valves connected to each of
the pressure chambers. The valves are of on/off-type
which means that they can only be fully opened or
closed. To be able to control the cylinder it’s necessary
to have appropriate sensors. On the test stand there
are a position sensor, accelerometer and three pressure sensors. These sensors give enough data to carefully control the cylinder. All the sensors and valves
are connected to the electronic box where they are
transformed and connected to a computer through a
measure card.
500
400
300
200
100
System layout
0
Controller
The control concept used in this work is state observer
with position, velocity and jerk feedback. These three
feedbacks give much information about the motion of
the shuttle which is necessary for a accurate control.
The whole controller is divided in three separate modules: Controller, PWM-modifier and PWM-generator.
Controller module contains algorithm for the controller. Since solenoid on/off valves can not be fed by continuous controller signal it has be transformed. Transformation of the signal is done by PWM-modifier and
PWM-generator.
PWM-modifier calculates the valve open time and
PWM-generator generates a complete PWM signal
which describes air flow through valves.
0
5
10
15
20
25
time[sec.]
PWM-Modifier
PWM-Generator
Plant
35
40
45
50
Plot of position and reference position with a maximum
position error of 1 mm.
Shuttle
box
Test stand
Controller
30