Development of 3D Printer with Integrated [623417]

Development of 3D Printer with Integrated
Temperature Control System
N. Mir-Nasiri1, Md. Hazrat Ali1*, Syuhei Kurokawa2
1School of Engineering, Nazarbayev University, Astana, Kazakhstan
2School of Engineering, Kyushu University, Fukuoka, Japan
*Email: [anonimizat]

Abstract —This paper presents the conceptual design and
implementation of a cost effective 3D prototyping machine which
encompasses the design of mechanical, electrical & electronics
systems as well as integrated Software in order to create a workable prototype. The objective of this research is to design and develop a machine which is controlled by a computer and
capable of producing 3D solid representation of a CAD model in
plastic via plastic extruder. A XYZ axes system is developed in order to enable the machine to carry out the prototyping process efficiently and effectively. A control system for the stepper
motors and heating actuator are also developed to satisfy the
precision requirement of this machine. The total system covers the conceptual design, the development process and the integration of the mechanical system and electrical and electronic
systems of 3D prototyping machine. Main focusing point of this
paper is to design and develop the suitable temperature control system of 3D Rapid Prototyping Machine (RPM).

Keywords—ABS; RPM; extruder; filament; temperature
I. INTRODUCTION
3D prototyping machines are widely used in order to
develop a model before it is being manufactured. These types of machines are usually controlled by Numerical Control (NC). Numerical Control is defined as an operation of machine tools by means of speci fically coded instructions or
Computer Numerical Control (CNC) programming language to the machine control system [1]. Notable CNC
programming language such as G-code and M-code is widely
used to computerize an entire machining process or automation process. These programming languages can be used to define the position of the machine tools to move to, the translation speed of the machine tools, the change of machining tools and the dispensing of coolant and so on. There are various types of rapid prototyping machines that are available in the market. The technical points of some existing systems are discussed below.
A. R2C2 RepRap Controller Board
R2C2 RepRap controller board is widely used in 3D
prototyping machine. This controller drives the filament by rotating the shaft of the motor. If the lead screw has a 1 mm lead and the stepper motor requires 200 voltage pulses to complete a single revolution. Thus, in order to achieve a travel distance of 100 mm, 20000 voltage pulses is applied to the stepper motor control. The microcontroller then convert the
pulses into travelled distance by using equation (1).

Fig. 1. R2C2 Controller's Allegro A4988 stepper driver

Figure 1 shows motor driver with other integrated circuits.
The R2C2 RepRap controller board is designed using an LPC1752 ARM 32 bit microcontroller as shown in Figure 1 which has the capabilities to operate at 100 MHz thus allowing the microcontroller to process information at a higher rate compared to that of microcontrollers with 8 or 16 bit architecture [2].

Fig. 2. EndStop switches for RepRap.
The R2C2 RepRap controller board allows the usage of micro-switches as a work area boundary sensor as shown in Fig.2 .
B. MakerBot Replicator
Another type of 3D prototyping machine is MakerBot
Replicator. Figure 3 shows block diagram of PID controller used by the MakerBot Replicator’s controller board. From the MakerBot, the recommended settings for the Replicator’s PID controller is as stated in Table I. These parameters are determined using Ziegler-Nichols tuning method [3].
The authors would like to express their gratitude to Nazarabyev University for
funding them to develop this system as a requirement of the capstone project.

Fig. 3. Closed loop block diagram for temperature control.
Table I. PID controller parameters for 3D printer (Replicator)

C. Hewlett-Packard Design Jet 3D Printer
The HP Design Jet 3D printer is a 3D prototyping machine
developed by Hewlett-Packard for professional designers, engineers or academic staff who requires shorter development time of their prototype. This machine is based on similar electronic system used in normal printer due to the similar nature of the task accomplished in the both types of printer. This type of 3D prototyping machines usually requires an external system such a computer server to manage all the machining programs and post-processing of CAD models via Ethernet interface or the more common RS232 serial interface. Computer Aided Design (CAM) software such as INVENTORCAM or SOLIDCAM is used to do post processing of the design model which encompasses the process of simulating the machining process, optimizing the
tools used, and generation of the optimized tool path. The tool
path generated is then exported into G-code format and uploaded into the corresponding machine’s controller to perform the actual prototyping process. The HP Design Jet 3D printer uses a closed loop position control system to ensure the required precision is obtained, by coupling a high resolution encoder onto the DC motor to provide the necessary position feedback [4]. Using the closed loop dc motor configuration, the machine can be designed to work with larger loads and higher operating speed without incurring higher machine cost. Currently, the most common DC motor used in high precision positioning is the permanent magnet synchronous motor.
II.
CONCEPTULA DESIGN OF THE SYSTEM
After referring to the information from the similar and
commercialized products which had been discussed in the
literature review, around 280 mm length, 280 mm width and
250mm height building envelope will be a fair working space for the 3D prototyping machine which will be built in this project. Thus, in order to develop a 3D printer with 280 x 280 x 250 mm building envelope, the frame or the whole supporting body will have to reach an overall 800 mm to 1000
mm length and width of 500 mm to 600 mm height
considering the tolerance from others factors (HBP and Z-axis moving area). Thus, from the estimated machine size, it is possible to predict that the frame will be sturdy and stable enough since the base is wide and the height is fairly stable for
the frame design. During the frame design, the railing systems and XYZ
motion drivers are to put in consideration throughout the design. A fully supported rail is chosen as the XY axes
supporting railing system. While on the Z axis, rod rail is
preferable for vertical supporting structures due to its simplify installation and high efficiency during Z axis movement. High precision in the alignment is needed for the rail during the installation and lubrication of the railing system that will eventually smoothen and ensure the printing precision. A fully
supported rod railing system is used for the railing system for
smooth and sturdy XY axes movements which will compromise both printing precision and quality

Fig. 4. Conceptual design of 3D prototyping machine.
Figure 4 shows the overall conceptual design of the 3D prototyping machine with acceptable tolerances and sizes of the parts.
III. S
OFTWARE AND LOGIC DESIGN
A. Extruder Heater

Fig. 5. Extruder heater.

The extruder heating block comprises of an aluminium
mounting block and a 40W heating element which is rated at 12V. Similar to the heat bed, the power dissipated by this
heating element is controlled by varying the duty cycle of the
PWM applied by the microcontroller. Since a 12VDC is applied to this heating element, the control system for this system uses an N-channel enhancement mode MOSFET to control the power delivered as shown in Fig. 5. The IRF540 MOSFET will be used together with a 4N25S optical isolator
which will provide a gate voltage of 12V to the MOSFET
whenever a trigger signal is received from the microcontroller.
B. Electronics Heat Dissipation
Heat dissipation of the electronic components is an
essential aspect of this project to ensure the robustness of the system and prevent catastrophic failure of its subsystem. Heat
dissipation of the stepper motor drivers and the power
MOSFETs must be taken into consideration due to the long operation period of a rapid prototyping machine by installing properly sized heat sink as passive dissipater.
C. Power MOSFETs Heat Dissipation
Power MOSFETs dissipates a significant amount of heat
when switching or controlling a sizable current source due to
switching losses and internal resistance of the device. To prevent thermal damages, heat sinks are used to reduce the junction temperature to a manageable level as shown in Figure 6. Besides that, excessive heat alters the characteristics of
power MOSFETs which usually reduces the maximum current
output, the overall efficiency and the reliability.
The heat dissipation of a MOSFET is generally caused by
two components as shown in equation (2):

Equation (3) determines the overall power dissipation of
the switching MOSFET at maximum load and accounts for the
switching losses where TJ hot is the maximum permitted die
junction temperature, Tspec is the temperature at which in on
resistance is specified, C RSS is the reverse-transfer capacitance
and fSW is the switching frequency [5]. To determine the
maximum heat dissipation, the assumed maximum current
load was selected 10A, the input voltage was selected 12V and a switching frequency of 2 kHz. Other parameters of the equation are based on the IRF540 datasheet specifications.

Fig. 6. Electrical analogy for the heat distribution component.

Based on Fig. 6, the heat distribution in an electronic
component is analogous to Ohm’s Law in which current
represents heat dissipation, resistance represents thermal resistance and potential difference represents temperature difference. The following calculations assumes that the system operates under stagnant airflow conditions, the junction to
case thermal resistance, (R
θJC) is 1.15 °C/W and the case to
sink thermal resistance, (R θCS) is 0.5 °C/W. These estimations
can be obtained via the datasheet and should give a fairly realistic prediction of the heat dissipation characteristics. The heat sink used for this application has a thermal resistance of 1.1 °C/W. However, 1.54 /W will be used to account for the
spreading thermal resistance (40% raise due to point thermal
heat source). Since the junction temperature is within the reasonable operating range, the heat sink used is appropriate for this application.
D. Heated Bed Platform
Figure 7 shows the heated bed platform of the 3D
prototyping machine. The heated bed platform is redesigned using a simple printed circuit board design. The copper surface produces heat when current flow through the PCB. However, the problem arises when the melted ABS does not adhere to the copper surface causing the whole model to be dragged along with the extruder leading to a prototype failure.
Several proposals were presented as a solution to the problem. Placing an aluminium plate or other metallic materials on the heated bed platform surface, the ABS adhering issue is still present and does not solve the problem. Further testing confirms our hypothesis that the ABS does not adhere properly to metallic surfaces. Initially, the aluminum plate was finally replaced by a piece of wood which did not solve the issue. Finally, an acrylic is used for the testing. The melted ABS is able to adhere firmly on the surface of the acrylic. Unfortunately, the acrylic sheet deforms due to the high temperature of 90°C from the heated bed platform. There were made several others attempts, such as using a thicker acrylic (1 cm thickness) sheet, a compact disc surface, and several other plastic elements. In addition, all of them failed to produce the desirable effect. However, our finding shows that the ABS plastic adheres on surfaces which are of plastic elements. Using the new findings, it was decided to tape a cheap vinyl sticker, which is a type of plastic, on the heat bed surface. As a result, the ABS plastic adheres fairly well to the vinyl layer and increases the chances of a success. Unfortunately, after several prototypes, the vinyl layer needs to be replac ed due to
its poor durability which results in tears on the vinyl sticker.

Fig. 7. Heated bed platform.
E. Extruder Mounting and Positiong
The extruder is mounted on two pieces of L-profile
aluminium bar. The L-provides aluminium bar is tough and does not bend when exposed to heat or humidity over a long
period of time. Since the 3D prototyping machine uses fused
deposition method, the material is melted and extruded out to form the model layer by layer, thus no external forces were introduced that may cause bending on the Z axis structures as compared those found on CNC milling machine. Hence, the two L-profile aluminium bar is sufficient enough to support
the extruder’s weight during the prototyping process. The tip
of the nozzle is required to be suspended at least 0.8mm from the heat bed. This is to ensure the extruded ABS plastic is able to adhere on the surface of the heated bed platform. Thus, an infrared (IR) sensor is located on the Z axis to act as a position
sensor or boundary limit switch in this case. Whenever the IR
sensor received a signal, the Z axis will stop moving
indicating that it has reached the required height above the surface of the heated bed platform. Any further movement towards the heat bed platform will potentially damage the heating surface and also the extrusion nozzle forces were
introduced that may cause bending on the Z axis structures as
compared those found on CNC milling machine. Hence, the two L-profile aluminium bar is sufficient enough to support the extruder’s weight during the prototyping process.
F. Safety Considerations
A safety cage has been constructed to cover the 3D
prototyping machine in order to distance the users from the heating elements during the prototyping process. This is to ensure that users do not disrupt the machine when it is in the prototyping process which could harm the users. Even though the heat bed platform have a constant temperature of 90°C, it is still relatively safe to touch the platform. However, the extrusion nozzle which is maintained at a temperature of more than 200°C is unsafe for the user to touch it. Hence, it is appropriate to build a safety cage in order to promote safety prototyping procedure.
IV. D
ESIGN OF EXTRUDER CONTROL SYSTEM
Concurrent object-oriented programs are slightly more
difficult to design, implement and maintain than sequential programs. During the design phase, meticulous attention has
been given in this aspect to reduce the likelihood of the complete redesign of the entire software’s architecture.
Suitable programming language is incorporated to this
software design in order to realize the following features:
¾ Real time temperature monitoring
¾ Prototyping completion rate display
¾ Motion control
A. Temperature Control System
Based on the temperature profile of both extruder and heat
bed as shown in Figs. 8 and 9, ground noise induced by the switching circuit of this system greatly affects the overall performance of the temperature sensor. The ground noise of the system is probably caused by the resistance of the ground
wire which carries more than 10 amperes of current which are
drawn by the heating systems and the 4 stepper motor drivers. Besides that, the poor common rejection mode ratio of the type-K thermocouple amplification circuit failed to isolate the ground noise and the signal voltage. From Fig. 8, ground noise leads to an increase of 15 °C from the steady state temperature
of 200 °C. A calibrated multimeter with thermocouple support
is used as an external measurement method to validate the temperature readings.

Fig. 8. Extruder temperature profile.

Fig. 9. Heat bed temperature profile.
In order to measure the ground noise of the system, we have setup the oscilloscope as shown in Fig. 10 where the signal
probe is connected to the ground of the system and the probe

ground is connected to the ground of the power supply. This
setup allows us to determine the overall signal noise induced in the ground wires.

Fig. 10. Oscilloscope setup.

Figure 11 shows a peak signal noise of 40 mV RMS at
approximately 375 kHz on the thermocouple signal amplifier circuit. This will severely affects the accuracy of the
temperature reading as the noise signal will be amplified
together with the thermocouple signal.

Fig. 11. Ground noise on thermocouple signal amplifier and the FFT analysis
of the sampled signal.

Based on the Allegro A4985 datasheet which is also
shown in Fig. 12, the stepper driver IC’s internal chopper
circuit which is used to regulate the current drawn from the
stepper motor.

Fig. 12. Allegro A4985 switching characteristic and timing chart.

The internal PWM current control circuitry uses a one-shot
circuit (mono-stable multi-vibrator circuit configuration) to
control the duration of time that the DMOS FETs remain off.
The off-time, tOFF is determined by the RO SC terminal as shown in Fig.12. From Fig. 13, ground noise induced by the
heating control system has been ruled out. The 1-2 KHz control signal of the heating system does not introduce
significant noise to the system based on the FFT signal
analysis.

Fig. 13. Control signal waveform of the heating system.

From equations (7) and (8), the conclusion can be drawn
that the stepper motor driver IC contributes to a significant
portion of the ground noise which has been affecting the overall performance of the type K thermocouple amplifier circuit. Fortunately, the effects of the ground noise are rather consistent and predictable over the course of time. To
compensate for this problem the set point temperature has
been lowered by approximately 15 °C to achieve the required temperature of 200 °C.
B. Heat Bed and Extruder Heater Control System

Fig. 14. Block diagram of the thermal control system.

Closed loop control of the thermal system is required in
order maintain the optimum extrusion temperature of about
200șC and a heat bed temperature of 100șC. Figure 14 shows the block diagram of the control system of this 3D rapid prototyping machine. By utilizing equation (6) and the NIST numerical model for thermocouples, a PID controller has been
developed to provide the best control for this system.

ADC
Microcontroller
Amplifier Thermostat Heat Plate PWM Heating
Element Set temperature Output temperature

C. Linear Motion System
This section will discuss on the mathematical aspects used
in developing the linear motion system. For the following
equations (9) to (12), the linear distances are represented in
number of pulses and the linear speeds are represented in the pulse rate.

The linear motion control system is an essential part of the
system which allows the system to position the extruder at the correct position and adjust the movement speed of each individual axis corresponding to the angle of motion and the
average movement speed. The pulse rate and number pulses to
reach a specific position at a suitable velocity can be calculated using axes finding formula. In addition, cumulative errors caused by precision loss during the conversion from a floating point number to an integer should be tracked and factored into the actual position. Precision loss is significant as
the system is highly repetitive which will lead to large
deviation.
V. P
ERFORMANCE EVALUATION OF THE CONTROL PARAMETERS
By simulating the block and apply PID optimization using
MATLAB’s SIMULINK toolbox as shown in Table II, we obtained the response as below. Integral windup issues due to
the saturation limits of the heat transfer function is also
included in the optimization by disabling the integral function until the process variable reaches the controllable region.

Fig.15. Temperature and thermocouple output voltage against time for
extruder heater.

Referring to Fig. 15, the thermal system has a settling
time of about 71 seconds or approximately 1.2 minutes with
an overshoot of 6.5%. For this application, overshoot of the
control system is the least important aspect in comparison to the settling time due to the usability criteria. The system should heat up as fast as possible in order for users to commence prototyping their product in the shortest possible
time frame.
Table II. PID tuning parameters for Extruder Heater

VI. CONCLUSION

In conclusion, the development phase for the electronics
and control system for the 3D prototyping machine is completed. In general, the electronics and software system in this application have achieved the project objectives and goals. Based on various tests conducted on the developed rapid prototyping machine, the mechanical system and the electrical system worked as expected with respect to the CAD drawings and design. However, it is believed that the quality of prototype created by the machine can be further improved by using a material with a lower glass transition temperature.
VII. F
UTURE WORK
To improve the functional requirement aspect, several
major microcontroller firmware changes are required. The current firmware varies the speed on each individual axis by changing the timer compare to register of the built-in pulse width modulation module in the PIC microcontroller. In order to provide better control over each of this axis, the proposed
new firmware should use time division based method in which the microcontroller centralized all the controls of the axis using a single timer instead of decentralizing the control over
to the PWM module. For the non-functional requirement aspect, a SD card module and a LCD module can be added to the controller to create a standalone system without the need for a PC or laptop connection. This will improve the usability aspect of the developed system.
R
EFERENCES
[1] Smid, P., 2003. CNC Programming Handbook. 2nd ed. s.l.:I ndustrial
Press Inc.
[2] Team, R., 2010. CAM Toolchains. [Online],Available at:
http://reprap.org/wiki/Comparison_of_RepRap_Toolchains [Accessed
23 2 2012].
[3] Industries, M., 2012. MakerBot Thing-O-Matic 3D Printer Kit –
MakerBot Industries.
[4] Suh, S.-H., Kang, S.-K., Chung, D.-H. & Stroud, I., 2008. Theory and
Design of CNC.
[5] Design, E., 2002. Calculate Dissipation For MOSFETs In High-Power
Supplies. [Online] Available at:
http://electronicdesign.com/content/topic/calculate-dissipation-for-
mosfets-in-high-power-su/catpath/power [Accessed 2 October 2012].