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Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 132 (2015) 118 – 125
The Manufacturing Engineering Society International Conference, MESIC 2015
Azara: A new 32 bit RepRap with improved performance A. Guerrero-de-Miera,*, M.M. Espinosaa, M. Domíngueza a
Design Engineering Area – UNED, c/Juan del Rosal, 12, Madrid 28040, Spain
Abstract RepRap Community was founded by Adrian Bowyer at the University of Bath in 2004. This initiative has promoted designs of several low cost open source 3D printers, and has proven very successful. RepRap printers' firmware is based on 8 bits microcomputers, and an external computer is needed to process 3D models and send it to printers (by USB or SD card). We have built a RepRap variant (RepRap Azara) that doesn´t need external computer, using a 32 bit ARM microcomputer (Beaglebone) and developing software and firmware able to process 3D models and to communicate through a web interface, all of it in the same costs' range. © by Elsevier Ltd. by ThisElsevier is an open Published Ltd.access article under the CC BY-NC-ND license ©2015 2016Published The Authors. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of MESIC 2015. Peer-review under responsibility of the Scientific Committee of MESIC 2015 Keywords: RepRap; Beaglebone; slicing method; web server; 3D printing
1. Introduction 3D printing technologies have experienced an important increase in popularity, due to the irruption of new low cost models in the market, with a medium to high performance. The spark that causes this expansion was the RepRap initiative, founded by Adrian Bowyer at the University of Bath in 2004[1]. This initiative has achieved to design and build many 3D printers, published under the “Do It Yourself” philosophy. These printers are partially self-replicant, and are Open Source because they are registered under a GPL version 2 license. RepRap printers uses Fused Deposition Modeling (FDM)TM technology, which build 3D models warming and extruding thermoplastic through a nozzle[2].
* Corresponding author. Tel.: +34 678 417 791 E-mail address:
[email protected]
1877-7058 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of MESIC 2015
doi:10.1016/j.proeng.2015.12.487
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RepRap printers hardware includes an electronic controller based on ATMega[3], a family of 8 bits microcontrollers. An external computer is needed to process 3D models and send it to printers, usually through a direct USB connection, although it can also be done using a SD card in some printers.
Fig. 1. 3D printing process
Our goal was to eliminate the need for that external computer, developing a RepRap variant printer with an electronic controller able to process 3D models alone, and to communicate through a web interface with printer's users. 2. 3D Print process 3D printing process involves a computer and a printer, and follows these basic steps[4] (see Figure 1): 2.1. Obtain a 3D Model in STL format User must build or obtains a 3D model. This 3D model must be converted to a STL format (developed for a stereolithography machine in 1988[5]). There are many websites sharing 3D models for accessories, toys, tools, etc. 2.2. Transform STL file in GCODE commands Then, the STL file is processed. Model is sliced in thin layers, usually of a constant thickness. Deposition paths are computed to build every single layer, from bottom to top, including borders and solid or filling surfaces. Those paths are transformed into GCODE commands, and saved into a file (normally with a “.gcode” extension). GCODE is the common name for CNC machines programming languages, and RepRap machines have their own quasistandard GCODE, with minimal differences among existent firmware models. There are several open source applications that process STL files, like Slic3r[6] or Skeinforge[7]. These applications must be used in a personal computer, existing variants for Windows, Linux and Mac OS X. 2.3. Send GCODE commands to 3D printer 3D printer machines have software resident in the printer electronic controller, connected to stepper motors, thermistors, heaters, etc. This software is called firmware. The GCODE file is sent to 3D printer. The firmware accepts commands form USB line, or through a SD card if printer has a SD card reader. The firmware interprets GCODE commands, building 3D models. There are a few open source firmwares for RepRap machines, like Sprinter[8], Teacup[9] or Marlin[10]. 3. Our proposal: a connected machine We wanted to change the functional schema of RepRap printers. Currently, you can only access to printer from one single computer, through a USB connection (see Figure 2). That external computer is needed for process STL files and transforms it into GCODE commands. In addition, the external computer is necessary to manage the printer firmware configuration, storing source code and compiling it after each change.
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Fig. 2. Current functional schema.
Fig. 3. Proposed functional schema. Table 1. Features of new RepRap controller. Feature
Minimal requirement
Interface
Ethernet and HTTP server
Disk size
>100MB
Input ports
3 digital & 2 analog
Output ports
14 digital
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Fig. 4. Beaglebone.
You cannot access printer from more than one computer, and if you want to send 3D models from others computers, you must use SD cards If we install a HTTP server inside the RepRap machine, we could access to the printer from any computer, even from a smartphone or tablet (Figure 3) and through internet. To do this, we had to change the electronic controller for another more powerful, with a web server inside. In addition, to eliminate the need of an external computer, we must translate the process of STL file into the printer firmware (step 2.2 above). We had to select a new microcomputer for firmware, with a GPL compatible license and specifications indicated in Table 1. Moreover, its price should be low, in order to keep the printer cost down. So, the new microcomputer for the RepRap firmware should have the following features: 1) An ethernet port and a HTTP server. 2) Enough memory for storing STL files and GCODE files (about 100 MB) 3) Computing capacity for transform STL files into GCODES. 4) Connectivity for stepper motors (12 digital output), heaters (2 digital output), endstop sensors (3 digital input) and thermistors (2 analog input). 5) License compatible with RepRap GNU Public License. 6) It must be affordable, not representing an extra cost. Our choice was the Beaglebone of Beagleboard.org[11]. It is a credit card size microcomputer with a 700 MHz ARM Cortex-A8 microcontroller and 256MB of RAM memory (Figure 4). 4. Building of the new RepRap Azara We have built a new RepRap variant with a new electronic controller based on a Beaglebone. First, we have built a standard RepRap Prusa 2, adquired in RepRap BCN[12]. Then we change the original controller by our own solution. The solution includes the following parts: We wanted to change the functional
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Fig. 5. Expansion board for Beaglebone.
4.1. Expansion board for Beaglebone Expansion boards are necessary to connect microcomputer to stepper motors, thermistors, heaters and endstop sensors. There are many expansion boards for existents electronics, but we need to build a new one compatible with Beaglebone. We have developed an expansion board for Beaglebone with the help of Electronic Engineering Group of University of Seville (GIE, TIC-192) (Figure 5), based in RAMPS 1.4[13]. Like most of existing expansion boards, our board uses Pololu A4988 drivers[14] to handle up to 4 stepper motors. It also has connectors for up to 6 endstops, up to 2 heaters, up to 2 thermistors and a fan. The new expansion board could be divided in five separate circuits: 1) Endstop inputs 2) Thermistor inputs 3) Motor drivers circuit 4) Heaters outputs 5) Fan circuit Due to space limitations, we have divided the expansion board in two parts, with a hole with fan in superior board to cool motor drivers. 4.2. Software to interpret GCODE commands The new controller needs new software. So, we have had to develop new software to interpret GCODE commands. The new interpret is written in C, with multithread features to control temperatures. For motor movements, we have written a module using the Programmable Real Time Unit in Beaglebone[15], to ensure correct movement speeds and accelerations. This module is written in assembler, and is controlled by interpret through shared memory. Our application works as a normal UNIX program, reading GCODE commands from the standard input and sending messages to users through standard output. We have added new GCODE commands to control the print queue.
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Fig. 6. Web user interface (initial tab).
4.3. Software to process STL files There are open source applications to process STL files (see 2.2 above), but we have preferred to develop our own application to improve control of movements. We have developed a C++ software application to process STL files and transform it into GCODE commands, only using Clipper as external library[16]. Our application processes STL files, following these steps: 1) Initial setup: generate patterns, load model and compute auxiliary models for solid faces and fill zones. 2) Slice layers, computing deposition paths. 3) Transform deposition paths into GCODE commands, sending to standard output. 4.4. Web server We have developed a web server, using node.js[17] and express framework[18]. We have chosen node.js due to his small size and usability. Our web server works like a UNIX service, starting when the controller is powering on. The web server starts a single instance of interpret of GCODE (4.2 above). The server receives direct commands from web users, including uploading of STL files or GCODE files. GCODE files are sent directly to print queue, and STL files are processed before. Direct commands are sent to interpret. To be able to send broadcast messages, we use socket.io library[19]. With this library, web server can receive commands from any connected user, and interpreted outputs can be sent back to all connected users. So, users no need to refresh web page to watch actual status of RepRap machine. The user interface is built with a tabbed page, with tabs for movements commands, motor commands, print queue, temperatures control, input and output messages and calibration.(Figures 6 and 7)
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4.5. Name and Logo RepRap machines usually have names of eminent naturalist, related to Theory of Evolution. So, our machine was named Azara in memory of Félix de Azara, a Spanish naturalist of XVIII century. The Azara logo represents a beagle dog (for Beaglebone) using a collar with RepRap logo (see Figure 8).
Fig. 7. Web user interface (print queue).
Fig. 8. RepRap Azara logo
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5. Conclusions We have built a new RepRap variant, including a web server with a complete user interface. Our RepRap Azara doesn’t need an external computer. It can be used by a smartphone or tablet, and accessed directly through internet. Our solution could be useful to share a printer among several users, like in offices or classrooms. In fact, it is an ideal regarded alternative to work in 3D printing in academic settings with distance methodology. In addition, web server could be modified to help in remote diagnostics, remote administration, e-learning, etc., which implies an advanced step in remote maintenance of the system. Acknowledgements We thank to Electronic Engineering Group of University of Seville (GIE, TIC-192) for his contribution in Beaglebone expansion board References [1] A. Bowyer et al. Reprap: the replicating rapid prototype. Robotics, vol. 29, nº Special Issue 01, (2011) pp. 177-191. [2] L. Romero et al, Additive manufacturing with RepRap methodology: current situation and future prospects. 25th Annual International Solid Freeform Fabrication (SFF) Symposium, 2014, University of Texas. Austin. [3] Atmel. ATmega128. www.atmel.com/devices/atmega128.aspx. [4] A. Guerrero-de-Mier, M. M. Espinosa Escudero. "Progress in RepRap: Open Source 3D Printing". DYNA 89, no. 1 (2014). [5] 3D Systems, Inc. Stereolithography interface specification, P/N. 50065-S01-00, 1989. [6] A. Ranellucci et al, Slic3, G-code generator for 3D printers. 2011-2015. http://slic3r.org. [7] E Pérez. (2009). Skeinforge, http://fabmetheus.crsndoo.com [8] K Yanev. (2010). Sprinter, https://github.com/kliment/Sprinter [9] T Hunter. (2010). Teacup, https://github.com/Traumflug/Teacup_Firmware [10] E van der Zalm. (2011). Marlin, https://github.com/ErikZalm/Marlin [11] Beagleboard.org. (2012). Bone, http://beagleboard.org/bone [12] RepRap BCN. (2012). Reprap bcn, http://www.reprapbcn.com. [13] J Russell. (2010). Ramps, the reprap arduino mega pololu shield. http://reprap.org/wiki/RAMPS_1.4. [14] Pololu Robotic & Electronic. A4988 Stepper Motor Driver Carrier. https://www.pololu.com/product/1182 [15] Texas Instruments. Programmable Realtime Unit Software Development. http://processors.wiki.ti.com/index.php/Programmable_Realtime_Unit_Software_Development [16] A. Johnsson. Clipper – an open source freeware library for clipping and offsetting lines and polygons. 2010-2014. http://http://www.angusj.com/delphi/clipper.php [17] Joyent, Inc. Node.js. http://nodejs.org/ [18] Strongloop, Inc. Express. Fast, unopinionated, minimalist web framework for Node.js. http://expressjs.com/ [19] G Rauch et al. Socket.io. http://socket.io/
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