Control System s with PLC for thermoplastic [627468]

1
Control System s with PLC for thermoplastic
extrusion

Bogdan -Ioan Bustan , Iulian -Andrei
Găină, Ciprian -Gheorghe Bila,
Gheorghe Golban, Ioan -Florin M ătieș
Department of Automation
Techni cal University of Cluj -Napoca
Cluj-Napoca, Romania

Abstrac t—Given the fact that manufacturing require s more
and more tools to satisfy the high standards of today’s industry,
the work horses of production, the CNC machines , are equipped
with more diverse tools than ever before. One of the most recent
tools added to these machines is the thermoplastic extruder for
additive manufacturing. Three -dimensional printing with
thermoplastic extrusion is one of the fastest growing industrial
prototyping tools. With more and more advanced CNC machines
and stepper -motors and im proved methods of control additive
manufacturing is taking steps into the field of industrial
production .
Keywords —CNC, PLC, thermoplastic extrusion, stepper –
motors, control .
I. INTRODUCTION
Being in the centrury of speed each part of our daily lives
is be ing aided by means of techo logy. By trying to ease our
work , more and more tasks are being transfered to technial
machines. Automation is introduced in the earlies t stages of
project development having an active role even in
prototyping. [8][9]
Additive manufactu ring with three -dimensional printing
is present in most of the research centers in the world where
rapid prototyping helps new ideas come to life. Most of these
printers use CNC machines and thermoplastic extrusion. NC
machines have been present since the end of the Second
World War being fi rst used in the aerospatial production
starting as two -dimensional machines making the step
toward three -dimensional application s in 1952 with the first
milling machines with bona fide numerical control. 3D
printing is a technology that appeared in the middle of 20th
century in research. Nowadays this technology is more
spread then ever with hobbyists and makers bringing
improvements and ease of access to everyone. The evolution
of this field offers more and more precis e solutions, some
technics of printing being rivals to traditional CNC milling.
[1]
The effort of this paper is the control of thermoplastic
extrusion using CNC controlled axis to position the printing
head, also known as extruder. This proccess is defined by a
heating element that melts the plastic used as filament. For
improved solutions a heated printing bed is used . The control
of the system is done using specialized drivers for the
servomotors of the CNC machine and the stepper -motors of
the printing h ead and power electronics for the temperature
control . The user interface of the aplicati on is done through
an OPC client. The same interface is used for process
tracking and high level control. [2]
In the picture below there can be seen the physical
syste m used to implement the technologies described in this
paper.

Fig. 1. CNC machine for thermoplastic extrusion
II. HARDWARE STRUCTURE OF THE CONTROL SYSTEM
A. CNC control structure

Fig. 2. CNC control structure
The components used in controlling the CNC , found in
the schematic above, are:
 PC: used for sof tware implementation, servo -driver
configuration and graphical interface;
 PLC: used to control the positioning system through
the developed software, the PLC being used is
CJ2M -CPU11 by OMRON;
 Driver: used to control the servomotors being called
SmartStep2 R7D -BP01H by OMRON ;
 Motor: used to rotate the shaft in order to position
the ball screw through the elastic coupling. The
motors used are OMRON -G10030H -S2;

 T: incremental position transducer used to measure
the speed and position , also closing the control
loops . [3]
B. Thermoplastic extrusion control structure

Fig. 3. Thermoplastic extrusion control structure
The components used in thermoplastic extrusion control ,
found in the schematic above :
 Amplifying stage: used to actuate systems that run
on high power, with galvanic separation in such
manner that the output of the controller is not
affected by the heating elements. The element used
for implementation is the G3NA -210B -UTU 5 –
24DC solid state relay by OMRON ;
 Printing head: used to heat the plastic filament that
is the raw material for print ing. The printing head
used is the MK8 ;
 Printing bed: used for structural enhancing of the
printed object;
 Temperature sensor: used to close the control loop
through an NTC 100Ω;
 Motor driver: used to control the stepper -motor,
with the L298N driver being integrated;
 Stepper -motor: used to control the amount of
filament being pushed through the printing nozzle.
The motor being use d is called 42BYGHM810
being a NEMA 17 stepper motor.
C. CNC single axis control

Fig. 4. CNC single axis control
In order to control one of the axis certain modules are
being used to make the physical connection . The PLC
through the I/O module MD211 -212 and the cab le XW2Z –
200J -B32 and the XW2B -40J6 -9A wire terminal block is connected to the servo -driver CN1 which commands the
servomotor.
D. Heating elements control

Fig. 5. Heating elements control
The control of the heating elements is made from the
PLC through the digital output module OD212 figured above
with DO_1 and DO_2 . The temperature values are being
read through the analog input module AD04U figured with
AI_1 and AI_2. [4]
E. Stepper -motor control

Fig. 6. Stepper -motor control
The stepper -motor used to control the quantity of
filament being extruded is commanded through a motor
driver, L298N, capable of driving both DC motors and
stepper -motors . [4]
III. SOFTWARE STRUCTURE OF THE CONTROL SYSTEM
To control the system a PC is used that communicates
with the PLC through OPC. In the sc hematic below the can
be seen the high level architecture. Also the control loops for
speed and position which are discussed in the next section.

Fig. 7. High level architecture

Fig. 8. Speed control loop of a CNC axis

Fig. 9. Position control loop of a CNC axis

A. OPC Inte rface
To implement a human -machine interface in systems
that use PLC most of the time the OPC standard is used to
communicate between devices. The OPC architecture is
composed of servers and clients. In or der to use OPC in our
system we use the CX -Server t ool of OMRON as a server
and a custom build OPC client in Python using OpenOPC
library. In such manner we can control and observe the
parameters of the system in a graphical user interface.
This structure is commonly known as SCADA in bigger
industrial pr ojects. [6]

Fig. 10. Graphical user interface
B. Position and s peed control
The position control is based on cascaded control loops
for both current for torque and speed. It uses a notch filter to
eliminate frequencies that induce vibrations in the
mechanical system . Also for position there can be seen that a
feed-forward loop has been implemented.
The first step in controlling the speed and position of the
axis is to c onfigure them with the CX -Drive tool in the CX –
One program bundle from OMRON. [6]

Fig. 11. Parmater config uration in CX -Drive
Also at same step we can add alarms in order to avoid
errors and faults for the system, e.g. overload alarm.
The software instruction which drives the motor is called
PLS2(887) and takes the following parameters:
 P – output port;
 M – output mode;
 S – first word of the settings table;
 F – first word of starting frequency.
The settings table contains the acceleration and
deceleration rate, the maximum target frequency and the
number of pulses. The frequency of the pulses start at the minim um level and are increased at every 4ms with the value
specified in the acceleration rate.
The values are found in specific memory addresses and
are set using the instruction MOV (021) .

Fig. 12. PLS2(887) ladder -logic instruction
The speed and acceleration are based on the relations
below:
Rotation speed:

(1)

Rotational a cceleration :

(2)

C. Thermoplast ic extrusion control
To control the temperature we first need to read it. To do
so we use a thermistor. Thermistors are resistors whose
resistance changes with temperature. An NTC thermistor like
the one used in this project will have its resistance decrease
with the increase of temperature. The relationship between
resistance and temperature is not linear but it can be
appro ximated using the beta equation: [4]
(3)

Where T 0 is 25oC and R 0 is the resistance of the
thermistor at 25oC. To use the thermistor with a controller a
voltage is required that can be measured by the ADC. In our
case the AD04U module is capable of reading such values .
The control method used in this project is the bi –
positional control with hysteresis . The command is on as
long as the temperature is below the set point and the
command is of f as long as the temperature is above the set
point taking in account the values of the hyste resis.
Considering both of the heating elements as pure ohmic and
the following relations:
(4)

(5)

We obtain the following:

(6)

Fig. 13. Process value handling in PLC [7]
When temperature is within certain optimal values the
plastic filament is pus hed through the nozzle for
thermoplastic extrusion.
IV. TEST AND VALIDATION
The following results have been obtained using the
methods and hardware described above:

Fig. 14. Printing head temperature

Fig. 15. Printing bed temperature

Regarding the position, using the co nfigurations showed
above the system functions with a precision of 0.1 mm.
V. CONCLUSION
The paper’s objective to prove that thermoplastic
extrusion can be done with industrial equipment has been
achieved. The purpose for future is to improve both the
preci sion of the CNC axis and also to study more the
temperature control, a field yet to be fully grasped and
controlled. Temperature control will be improved by using
commands in frequency.
VI. BIBILOGRAPHY

[1] S.-H. Suh, S. K. Kang, D. -H. Chung și I. Stroud, „Introduction to NC
Systems,” în Theory and Design of CNC Systems , Springer, 2008, pp.
3-14.
[2] C. Bailey et. al, “Augmenting computer -aided design software with
multi -functional capabilities to automate multi -process additive
manufacturing” , IEEE, February 2018.
[3] ***** Omron, „CJ2M CPU Unit Pulse I/O Module User’s Manual”.
Japonia Brevet W486 -E1-01, 2010.
[4] P. Scherz, S. Monk, “Practical electronics for inventors”, Fourth
Edition, McGraw Hill Education, 2016.
[5] G. G . Florea and L. A. Ochean, “ Towards total inte gration based on
OPC standards,” Information Control Problems in Manufacturing
IFAC, pp. 1 -6, 2012.
[6] ***** Omron, „CJ -Series CJ2M CPU Units”, 2017.
[7] ***** Omron, “SYSMAC CJ Series CJ1W -AD04U CJ1W -AD04U –
SL Univers al Input Units Operation Manual”, revised December
2007.
[8] ***** TTOnline, „Conferință europeană cu tema ,,Fabricația Aditivă
și Imprimare 3D ”, May 2018
[9] ***** 3D Hubs, „What is 3D Printing? The definitive guide to
additive manufacturing ”, May 2018