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# CAN Bus: The Future of Additive Manufacturing (3D Printing)

Jun-Cheng Chin  University of Tennessee, Knoxville, US  Himanshu Thapliyal
University of Tennessee, Knoxville, US  Tyler Cultice  University of
Tennessee, Knoxville, US

(2022)

###### Abstract

Additive Manufacturing (AM) is gaining renewed popularity and attention due to
low-cost fabrication systems proliferating the market. Current communication
protocols used in AM limit the connection flexibility between the control
board and peripherals; they are often complex in their wiring and thus
restrict their avenue of expansion. Thus, the Controller Area Network (CAN)
bus is an attractive pathway for inter-hardware connections due to its innate
quality. However, the combination of CAN and AM is not well explored and
documented in existing literature. This article aims to provide examples of
CAN bus applications in AM.

††journal: IEEE Consumer Electronics Magazine

Additive Manufacturing’s (AM) place in the manufacturing industry is
indisputable with the advent of low-cost solutions for parts fabrication,
often known to the masses under the alias "3D Printing". The cost of 3D
printing has dramatically decreased, leading to the advancement and widespread
adoption of this technology. According to [1], approximately 2.2 million 3D
printers were sold globally in 2021, with the market value expected to
increase by 20.8% between 2022 and 2030. The RepRap movement brought about a
revolution in AM with its mission of developing machines that clone themselves
with self-fabricated parts, cheap electronics, and servos [2]. As the name
would suggest, AM is a technique where the material is deposited in layers to
form a 3-D structure. The most popular type of 3D printer among enthusiasts
and professionals is one that utilizes the material extrusion process. Other
AM processes include binder jetting, directed energy deposition, material
jetting, powder bed fusion, sheet lamination, and vat photopolymerization.

Figure 1: General idea of 3D Printer with CAN bus.

The Controller Area Network (CAN) communication protocol is widely used in the
automotive industry, dating back to the early 1990s. Nowadays, the majority of
vehicles on the market implement CAN due to their robustness and reliability
[3]. Commercial vehicles may contain hundreds of Electrical Control Units
(ECU), or controllers, which operate the vehicle. CAN enable the integration
of all of these ECUs without incurring costs, speed, or integrity penalties.
Adoption of the CAN bus has also seen massive interest from the aerospace
industry [4, 5]. The goal is to replace or improve current communication
protocols to provide this reduction in cost, reliability, and functionality in
various embedded systems [6]. All of these benefits can be applied to simplify
and increase the utility of AM control systems.

Popular AM machines in the current market, sought by enthusiasts and labs, use
Fused Filament Fabrication (FFF) or Fused Deposition Modeling (FDM) type [7].
The 3D printer’s heart, or the microcontroller, is generally cost-effective
and has low processing power in nature. The basic job of a 3D printer
controller can be boiled down to servo or motor controls and temperature
detection. Serial Peripheral Interface (SPI), Inter-Integrated Circuit (I2C),
and Universal Asynchronous Receiver Transmitter (UART) are used for inter-
hardware communication and control. Table 1 provides a general rundown of
inter-hardware communications commonly used in 3D printers [8]. These devices
utilize point-to-point communication systems, requiring individual
interconnections for each implemented device. The complexity of upgrading the
system increases depending on its scale and functionality. Additionally, the
various sensors and motor drivers connecting to the platform require fast and
robust messages with low error tolerances.

The attractiveness of CAN lies in its integrity-based design, which can
achieve extremely fast data payloads. Fig. 1 gives an illustration of the
general idea of a 3D printer with a CAN bus. In addition, it is a multi-master
and multi-destination system all within a single bus, enabling avenues for
modularity or plug-and-play capabilities. The conventional 3D printer has an
exponential wire connection. With the CAN bus, the wire numbers will be
reduced to a constant number [9]. In effect, the CAN bus improves the ease of
modularity and part-cost disparity.

This article seeks to highlight and provide examples of CAN bus applications
in AM for different scopes and scenarios. We have considered four case
studies: (i) CAN bus integration within an Internet of Things (IoT) 3D
printing farm, (ii) CAN connected immediate part adhesion testing with a test
instrument add-on, (iii) mobile large-scale cement 3D printing with CAN, and
(iv) novel fiber orientation control using a CAN connected rotational print
head. The rest of this article is organized as follows: Section 2 goes through
a brief background of CAN, laying out the wiring configuration, message
structure, arbitration, and error correction mechanisms. Next, Section 3
highlights five examples of CAN bus applications in additive manufacturing.
Finally, section 4 discusses future research directions of CAN in AM and
concerns with the major adoption of the communication protocol.

## BACKGROUND ON CAN PROTOCOL

Figure 2: CAN wiring configuration [10, 11, 12, 13, 14]. Table 1. Comparison
between common communication protocols and CAN
---
Protocol | Complexity | Speed | No. of Wires | No. of Devices | No. of master & slave
UART | Simple | Slowest | 1 | Up to 2 | Single to Single
I2C |  | Easy to chain
---
multiple devices
| Faster
---
than UART
2 | Up to 127 , but gets complex | Multiple slaves & master
SPI |  | Complex as
---
device increases
Fast | 4 | Many, but get complex | 1 master, multiple slaves
CAN |  | Easy to chain
---
multiple devices
Fast | 2 | Many, but simple | All of them are Masters
Figure 3: Summary of Standard CAN message frame bit field[12].

The building blocks of CAN hardware design consist of a computing unit, a CAN
controller, and a CAN transceiver. Each connected device containing all these
components forms a CAN Node and communicates over a differential pair of bus
wires. Even as the node count increases, the multiplexed/arbitrated bus design
allows all CAN nodes to communicate along the same shared pair of wires, as
shown in fig. 2.

Conventional multi-wire loom connections, which span up to thousands of wires,
are reduced to a single bus with CAN. This also effectively reduces the price
of wires and the weight of the product, resulting in an overall reduction in
development costs. The two-wire bus uses a differential wiring mode (CAN-H and
CAN-L) that reduces wiring complexity, noise, and electrical interference in
noisy environments. Furthermore, the CAN bus’s effective distance correlates
with the data transfer rate. The CAN standard provides various maximum wire
lengths, from 40 m at 1 Mbps to 1 km at 10 kbps.

The standard’s specification details the structure of the message frame and
error/fault detection [15]. CAN message packets or frames have four fields:
arbitration, control, data, and cyclic redundancy check (CRC). These fields
must be assigned properly for successful CAN message transmission. Fig. 3
summarizes the standard CAN message frame with its bit field assignment and
purpose.

Unlike master-slave protocols like the I2C interface or SPI, CAN is a multi-
master serial communication protocol. This means every CAN node is allowed to
communicate with each other, regardless of hierarchy. In addition, all
messages are destination or message-ID based, as CAN arbitration will
broadcast them throughout the whole bus regardless of the source of
transmission. Thus, all nodes must actively ’listen’ to messages on the bus
but will only act when arbitration/ID criteria are met. While ID-based
arbitration contains no source checking or secure end-to-end communication,
this method is very attractive for data monitoring and multi-destination
purposes.

What makes CAN reliable rests in its built-in bit-wise arbitration and error
checks. Under the hood, bit-wise arbitration allows the nodes to choose
whether to ignore or accept the message based on the 11-bits of ID and the ID
mask. Additionally, dominant IDs can prioritize messages when two nodes
transmit data at the same time, with the unprioritized message attempting to
re-transmit shortly after. This is great as lower priority nodes automatically
retry transmission and do not waste resources. The error checking mechanisms
for CAN are performed on the physical and digital level[14]. Physical checks
are handled with an error confinement mechanism (ECM) within every node, where
faulty ones are disabled from the bus traffic upon detection. On the digital
level, the CAN specification details five error types: bit, stuffing, CRC,
form, and acknowledgement[15].

## CASE STUDIES REGARDING APPLICATION OF CAN IN AM

Advertisement of the general utilization of CAN for inter-hardware
communication by commercial 3D printer manufacturers is rare. One example is
the Snapmaker 2.0 by Snapmaker, a 3D printer that applies CAN for its 3-in-1
printing platform. Their machine is capable of Fused Filament Fabrication
(FFF), CNC milling, and laser engraving. Depending on the application, the
printer’s printing heads, along with its respective print beds, are easily
interchangeable. This model is a departure from the original that uses RJ45s
and RJ25s, which requires a point-to-point connection and a dedicated
connector for each component.

Reviewing the available literature, the adoption of CAN in AM is an emerging
topic and is very promising. The rest of this article sheds light on examples
of applications of CAN by different groups in AM.

### Case Study 1: 3D Printing Monitoring Platform Based On the IoT

Figure 4: 3D Printing Farm with CAN bus camera link [16].

A 3D printer farm is a large collection of printers designed with the
objective of mass producing what a normal printer is limited to. Depending on
the 3D model, material, and resolution, a normal print job could take roughly
10 minutes to more than 24 hours. It is imperative to monitor the status of
the printer and printed parts. Monitoring is compounded and made extremely
crucial as the system scales to the size of a farm. Every node of printers
must be observed to ensure maximum profit and time investment.

The main structure of a 3D printer farm features a central computer connected
to a hub of 3D printers and an operator to monitor the operation. In J.J. Wu
et al’s work, integration of the CAN bus as part of the data monitoring node
is demonstrated within a wireless network [16]. Fig. 4 shows an illustration
of a 3D printing farm with the CAN bus camera link. The multi-master nature of
the CAN protocol allows all nodes to broadcast all-in-one information within
the bus, which fulfills the objective of quality control. In addition, the
complexity of inner-printer connections is drastically reduced. However, the
limitations of their printers caused only a partial CAN solution where the
print quality is monitored via CAN-connected cameras.

### Case Study 2: Part Adhesion Measuring Device in FFF process

Figure 5: Model of FFF 3D Printer with Tensile Testing Machine by [17] is
licensed under CC BY 4.0.

The low cost and rapid prototyping of these printers are highly sought-after
by laboratories around the world. Depending on the print material, adhesion to
the bed surface may come into question. Despite the mass proliferation of
these printers, there do not seem to be standards that provide guidelines for
compatible materials for print bed adhesion.

Laumann, Daniel, et al. constructed a 3D printing machine with an integrated
tensile testing device [17]. The main goal is to directly test the adhesion
forces between the printed part and the print bed immediately after completing
a print. They chose to incorporate an all-in-one solution using the Duet 3
controller board and its CAN bus expansion board respectively for normal
operations of the 3D printer and tensile testing operations. The authors
express the ease of modularity with the CAN bus for the expansion of further
tasks. Fig. 5 shows a 3D render of the integrated tensile testing and 3D
printer.

### Case Study 3: Mobile Large Scale Concrete 3D Printer Design

Figure 6: Mobile Cement 3D Printer Concept [19].

Recently, the researchers in [21] list 42 architectural works utilizing
concrete 3D printing, and provided an exhaustive survey of the advantages and
limitations of this manufacturing technique. For example, Habitat for
Humanity, a prominent non-profit construction organization, is venturing into
the arena of 3D-printed houses [20]. The number of buildings constructed by
these companies points to the rapid adoption and commercialization of AM
within the construction industry.

A group of engineering students at the University of Surrey proposed a design
for a portable concrete 3D printer that is housed in a semi-truck trailer
[18]. Their proposed design is shown in fig. 6. This is an interesting idea,
as concrete 3D printing is akin to conventional 3D printing, which requires a
more delicate operation. Essentially, the locations of the print head, bed
leveling, and cement composite status have to be considered. The significant
difference between a conventional 3D printer and a cement 3D printer is the
size and print material. A CAN bus is capable of transmitting over huge
distances without compromising speed or data accuracy and is capable of
maintaining and monitoring the current status of the printer due to its
masterless nature.

### Case Study 4: Fiber Orientation Control via Rotational Print Heads in 3D
Printing

M.D. Roberts designed and implemented a prototype rotational print head to
control fiber orientation in 3D printing [22]. This process is called
Rotational Fused Filament Fabrication (RFFF), in which fiber orientation is
controlled by inducing rotational shear forces into the flow of material
through the nozzle. Fiber orientation is controlled through changes in the
shear rate, allowing for the printing of structures with targeted local
properties.

The main controllers used in this prototype are a combination of the Duet2
WiFi and the Hyrel 3D Hydra 16A control board. The Duet2 board is used for the
extruder control and rotational fiber orientation control, while the Hydra 16A
board is used for controlling the XYZ axis of the 3D printer system. By
inspecting the provided wiring diagram, data monitoring and syncing are
performed over the CAN bus where the status of rotation, temperature, and
filament are shared between the controllers.

## DISCUSSION AND FUTURE RESEARCH DIRECTION

The integration of AM with CAN has the potential to be the next step for the
normalization of its inter-hardware communication protocol. Users of AM span
from enthusiasts at home to professionals in laboratories around the world.
Upgrades are often sought-after for their equipment to expand their options of
what they can create. By using an AM system that has CAN as its main choice of
central communication, the users can take advantage of the modularity and ease
of data monitoring. Similar to how the automotive industry provides ECUs with
a lot of low-level functionality on the CAN bus, the robustness and ease of
use should be utilized in the AM market as well.

Even though CAN provides live, high-speed communication between connected
hardware, it still has disadvantages associated with it. The first drawback is
the CAN bus wire length to signaling rate limitation, with a recommended
maximum of 30 nodes. More nodes can be added, extending wire lengths and
causing trade-off considerations to signal rates [12]. Another issue is that
any physical access to the CAN bus provides access to its multi-destination
input and output. Thus, the CAN bus is also exploitable due to not having pre-
built provisions for authentication and confidentiality, which makes it
vulnerable[13, 14, 23, 24]. The march forward into future generations of the
manufacturing industry and the IoT are prone to security breaches which have
huge consequences. Any future applications with CAN have to check and cover
all vulnerabilities to safeguard lives, property, and the environment from
malicious entities.

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Jun-Cheng Chin is currently working toward the M.S. degree in electrical
engineering with the University of Tennessee, Knoxville, TN 37996, USA.
Contact him at<EMAIL_ADDRESS>
Himanshu Thapliyal is an Associate Professor with the Department of Electrical
Engineering & Computer Science, University of Tennessee, Knoxville, TN 37996,
USA. Contact him at<EMAIL_ADDRESS>
Tyler Cultice is currently working toward the Ph.D. degree in electrical and
computer engineering with the University of Tennessee, Knoxville, TN 37996,
USA. Contact him at<EMAIL_ADDRESS>