Position Control of a Pneumatic Cylinder Using On-Off Solenoid Valves in Combination with Programable Logic Controller

Control of a Pneumatic Cylinder Using On-Off Solenoid Valves in 
Combination with Programable Logic Controller 
Tran Xuan Bo 
 Hanoi University of Science and Technology - No. 1, Dai Co Viet, Hai Ba Trung, Hanoi, Viet Nam 
Received: February 04, 2020; Accepted: June 22, 2020 
Abstract 
This paper proposes an accurate control method for position of a pneumatic cylinder using on-off solenoid 
valves in combination with a programmable logic controller. In order to deal with this purpose, an 
experimental setup of the pneumatic system using a double acting pneumatic cylinder, four on-off solenoid 
pneumatic valves and a PLC siemens S7-1200 is considered. The control law is designed basing on the 
transitions between seven operating modes of the pneumatic valves and selection of the operating modes is 
depended on the tracking position error of the cylinder. The experimental results show the usefulness of the 
proposed control method. The pneumatic cylinder can track well the desired step position with a rise time 
less than 1 s, no overshoot and steady-state tracking errors less than 2 mm. 
Keywords: Pneumatic cylinder, on-off valve, position control, logic control, programmable logic controller. 
1. Introduction 
Pneumatic* and hydraulic transmission systems 
are commonly used in industrial automation 
applications such as ship steering systems, hydro 
turbine speed control systems, blade rotation systems 
of wind turbines and industrial robot systems,... due 
to their advantages on high power/weight ratio, high 
strength, safety and easy maintenance [1]. However, 
the characteristics of hydraulic and pneumatic 
systems are usually high-order nonlinear due to the 
nonlinearity of the valve, the compressibility of the 
fluid and the friction force. Therefore, precise control 
of the position and velocity of hydraulic and 
pneumatic actuators often faces many difficulties. 
To control precisely position of the hydraulic 
and pneumatic actuators, servo valves or proportional 
valves are often used. These valves allow continuous 
control of the flow into the actuator’s chambers and 
therefore the speed and position can be easily 
monitored. However, servo valves and proportional 
valves often have relatively high costs due to the high 
cost of manufacturing them. A cheaper alternative 
method to servo valves and proportional valves is the 
use of on-off solenoid valves. These valves are 
widely used in hydraulic and pneumatic transmissions 
and are generally available in the market. However, 
when using on-off solenoid valves, precise motion 
control is often difficult due to the valves' switching 
time and their digital open/close characteristics. 
Therefore, suitable control methods should be applied 
to improve the control performances of the system 
using an on-off type electric valve. 
*Corresponding author: Tel.: (+84) 914.785.386 
Email: bo.tranxuan@hust.edu.vn 
So far, several studies have applied on-off 
solenoid valves to control the position of hydraulic 
and pneumatic actuators [2-6]. In these studies, one to 
two on-off pneumatic solenoid valves were often 
used and therefore the control performances achieved 
in these studies were limited and the number of 
valves opening and closing times was often quite 
large. In this study, the author will propose a new 
method for improving position control performances 
of a pneumatic cylinder. To carry out this work, an 
experimental system and a suitable control method 
using four solenoid valves will be proposed. 
Experimental results with different reference inputs 
will be given to evaluate the proposed control 
method. 
2. Pneumatic system 
Fig. 1 shows the schematic of the pneumatic 
system and Fig. 2 shows an image of the 
experimental system considered in this study. The 
system consists of a double acting pneumatic cylinder 
(1) with bore diameter, rod diameter and stroke 
length of 20, 10 and 300 mm, respectively. The 
cylinder rod is connected to a external load M (3) 
moving on a guiding bar (4). To control cylinder 
movement, four pneumatic solenoid valves (6) with 
an on-off type AIRTAC 2V025-08 (2 ports, 2 
positions) are used. The valves are electrically 
controlled at one end and can provide flow rate up to 
100 l/min. The solenoid valves 1 and 2 are connected 
to the left-side chamber of the cylinder (Chamber 1) 
and thus compressed air can be supplied to the 
cylinder chamber via Valve 1 or discharged from the 
cylinder chamber by Valve 2. Meanwhile, the 
solenoid valves 3 and 4 are connected to the right-
side chamber of the cylinder (Chamber 2) and thus 
Journal of Science & Technology 143 (2020) 013-017 
14 
compressed air can be supplied to the chamber via 
Valve 3 or discharged from the cylinder chamber by 
Valve 4. Compressed air is supplied from an air 
compressor and through an air source preparation 
unit. A position sensor Novotechnik LWH300 (2) 
with an accuracy of less than 0.5% F.S is used to 
measure the displacement of the piston rod. The 
position signal is connected to an analog input chanel 
of a Programmable Logic Controller (PLC Seimen 
S7-1200). Electric control signals of the valves u1 to 
u4 are connected to the digital output chanels of the 
PLC. A computer (PC) is connected to the PLC for 
data acquisition and for programming the system 
control law. TIA Portal software is used for 
programing. The sampling time used in the control 
program is 0.1 second. Air source pressure is set at 6 
bar. 
M
PLC
x
Compressor
Chamber 1
Chamber 2
Air preparation unit
Position
sensor
PC
u2 u1 u3 u4
p ,
1 V1 p ,2 V2
p
s
Solenoid
valve
Fig. 1. Schematic of pneumatic system 
Fig. 2. Image of the experimental system 
3. Controller design 
It can be noticed in the pneumatic system that 
with four solenoid valves, each with two closed or 
opened states, there are a total of 16 separate modes 
to control the piston movement at a given time. 
However, one-cylinder chamber cannot be supplied 
or discharged air at the same time. In addition, two 
chambers of a cylinder cannot be supplied with 
pressurized air at the same time. Therefore, only eight 
remaining control modes are considered (Table 1). 
For M1 mode, all valves are closed (ui = 0, i = 1 to 4); 
with this mode, the cylinder piston can be fixed in 
one position. 
Table 1. Operating modes of the solenoid valves 
 M1 M2 M3 M4 M5 M6 M7 M8 
u1 0 1 0 0 0 1 0 0 
u2 0 0 1 0 0 0 1 1 
u3 0 0 0 0 1 0 1 0 
u4 0 0 0 1 0 1 0 1 
In M2 and M5 modes, only Valve 1 or Valve 3 
is opened to supply air into the cylinder chambers, the 
other three valves are closed. This can be considered 
as a case of reducing speed of the piston when 
approaching nearby the required position; these two 
modes depend on the compression ratio of the gas. In 
contrast, in M3 and M4 modes, only Valve 2 or Valve 
4 is opened to discharge air from the cylinder 
chamber, the three remaining valves are closed. The 
purpose of this mode is to reduce the speed and to 
reduce the pressure in the cylinder chamber before 
switching to M2 mode and M5 mode. For two modes 
of M6 and M7, one valve is opened to supply air to 
one-cylinder chamber and one valve is opened to 
discharge air from another cylinder chamber. These 
two modes are considered as the acceleration case for 
the piston when the piston starts moving. Finally, for 
M8 mode, Valves 2 and 4 are opened together and so 
this is also a case to stop the piston movement but the 
stop state of the piston is unstable; only a small 
change of the load will affect the piston position. In 
the eight above modes, there are two modes M1 and 
M8 which can stop the piston movement but the M1 
mode can provide a stop state that is more stable than 
that of the M8 mode. Therefore, only the stop mode 
M1 for the piston is chosen. So only seven modes 
M1, M2, M3, M4, M5, M6 and M7 are used to 
control the piston position in this study. 
Fig. 3. Schematic of the closed-loop control system 
 In this study, a controller is proposed basing on 
the switching state between the seven operating 
modes mentioned above of the four pneumatic 
solenoid valves. The diagram of the closed control 
system is shown in Fig. 3. The controller will act 
differently depending on the operating mode selected 
at any given time. For position control systems, the 
Journal of Science & Technology 143 (2020) 013-017 
15 
position control error e of the system is defined as 
follows: 
 de x x (1) 
where, xd is the desired control position and x is the 
actual position of the piston. Switching between the 
operating modes of the controller is decided basing 
on the control error e of the system. Seven intervals 
of error e are considered to select the operating 
modes as shown in Table 2 and Fig. 4. The idea here 
is that the error is divided into small intervals and at 
each position interval each mode is used respectively 
to open and close the valves accordingly. As shown 
in Table 2, if the error e  , it means that the error 
is within the largest range, the mode M6 is used for 
the positive direction of the piston and the mode M7 
is used for the negative direction of the piston. With 
these modes, the maximum flow rate can be supplied 
to or discharge from the cylinder chambers and this 
makes the piston move as fast as possible to the 
desired position to achieve the fastest possible rising 
time. When the error decreases and is within range 
e  , the M4 mode is used for the positive 
direction of the piston and the M3 mode is used for 
the negative direction of the piston to reduce the 
speed of the piston to prevent the piston from 
exceeding the desired position value that is caused by 
the piston inertia. When the error e decreases further 
and falls down within the range e  , the 
controller will switch to M2 mode for positive 
direction of the piston and M5 mode for negative 
direction of piston. Under these conditions, the piston 
moves slightly due to the compression of the gas. 
Finally, when the error is within the range of the 
smallest allowable error, the M1 mode is used to stop 
the piston movement. 
Table 2. Conditions for the operating modes 
Conditions Operating modes 
e  M6 (Valve 1, Valve 4 ON) 
e  M4 (Valve 4 ON) 
e  M2 (Valve 1 ON) 
e  M1 (4 valves OFF) 
e  M5 (Valve 3 ON) 
e  M3 (Valve 2 ON) 
e  M7 (Valve 2, Valve 3 ON) 
Fig. 4. Diagram of control modes 
Fig. 5. Control performance with a desired constant 
input (controller’s parameters =0.05, =0.035, and 
τ=0.002): a) tracking position; b) tracking error. 
4. Results and discussion 
In this section, experimental results with the 
desired control position xd, which are constants or a 
triangle wave, are given to evaluate the proposed 
control method. The controller’s parameters were 
selected as follows: =0.05, =0.035, and τ=0.002. 
These parameters were selected basing on the trial 
and error method so that the control performance is 
the best. Fig. 5 shows a control result with constant 
input xd = 0.15 m. It can be seen that the controller 
provides good control performances; in transient state 
Journal of Science & Technology 143 (2020) 013-017 
16 
the piston moved from the starting point of 0.02 m to 
the desired position of 0.15 m with a time interval of 
1.1 seconds. The result also indicates that there is no 
overshoot of the piston and in steady state the error 
obtained is 0 mm. 
The rise time of the piston in Fig. 5 depends on 
the maximum flow rate of the valves used. In 
addition, the rise time depends on the values of the 
controller’s parameters, especially the two parameters 
 and . When the value of  was reduced from 0.05 
to 0.03 and the value of  was reduced from 0.035 to 
0.025 and the value of τ = 0.002 was hold, a faster 
rise time of the piston can be achieved as indicated in 
Fig. 6. In this case, the piston displaces from 0 m to 
the desired position of 0.25 m in a period of 0.6 
seconds, but overshoot behavior occurs in transient 
state. Therefore, the displacement of the piston 
depends much on the selection of the controller’s 
parameters. 
Fig. 7 shows the control performance for the 
case that the piston tracks a desired triangle input 
with the amplitude ranging from 0.12 m to 0.22 m. 
Controller’s parameters =0.03, =0.035, and 
τ=0.002 are used. The results indicate that the piston 
can follow very well to the desired position in both 
the extending and retracting strokes of the piston. It 
takes 1 second for the piston to reach the desired 
position and overshoot occurs only when the piston 
start running. In later processes, the overshoot 
behavior is not observed. The largest position error in 
steady state is 1.85 mm. 
Fig. 6. Control performance with a desired constant 
input (controller’s parameters (=0.03, =0.025, and 
τ=0.002): a) tracking position; b) tracking error. 
Fig. 7. Control performance with a desired triangle input (controller’s parameters (=0.03, =0.035, and 
τ=0.002): a) tracking position; b) tracking error. 
5. Conclusion In this paper, a new method for precise position 
control of the pneumatic cylinder is proposed. Four 
Journal of Science & Technology 143 (2020) 013-017 
17 
two-position two-port pneumatic on-off solenoid 
valves were used and a logic control algorithm based 
on the seven operating modes of the valves was 
considered. Each cylinder chamber was connected 
with two valves to increase the control ability of the 
piston position Experimental studies was conducted 
and the experimental results indicated that the control 
method yielded high-precision control performances 
with fast rise times under 1 second and steady-state 
errors of less than 2 mm. 
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