Fab@Home:Model 1 Overview

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Welcome to the main page for the Fab@Home Model 1

Figure 1 - A Fab@Home Model 1 Fabber
Figure 1 - A Fab@Home Model 1 Fabber

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On this page (and on the pages it links to) you can find everything you need to put together and use your Model 1 Fab@Home desktop fabricator. If you know all of this already, or are impatient, then jump right in to building your own Model 1. Vous aimeriez vous procurer une perruque, mais vous souhaitez obtenir un résultat naturel qui vous ressemble? La Clinique Capillaire Lavallée offre tous les services dont vous pourriez avoir besoin en matière de perruques pour femmes.

Overall Design

The Fab@Home Model 1 (Figure 2(a)) is a 3-axis Cartesian gantry positioning system driven by stepper motors attached to lead screws in a configuration called a linear stepper motor. Material deposition tools are modular, and the first tool we have designed is a syringe-based extrusion tool which uses a linear stepper motor to control the syringe plunger position. The electronics of the current version of the system provide for 4 axes of bipolar stepper motor control at 24V, with 2 limit switches per axis of positioning, plus an optional one limit switch for the remaining 3 axes. The software and firmware support up to 6 axes of control in their current incarnation. A microcontroller controls the positioning of the axes and is in bidirectional USB communications with the PC. An application running on the PC displays the real-time state of the machine numerically and graphically, and allows the user to manually position the axes, import, assemble, and perform basic modifications to STL geometry data, apply specific material properties to each STL, and to generate and execute tool paths in order to fabricate objects comprising multiple materials.

Figure 2.  The Fab@Home Model 1 Design. (a) 3D CAD model of an assembled Model 1; (b) An example of assembly instructions
Figure 2. The Fab@Home Model 1 Design. (a) 3D CAD model of an assembled Model 1; (b) An example of assembly instructions

One concern in developing our design has been that there probably exists a threshold of quality required in any new technology kit for hobbyists, below which the excitement of the new technology will be masked by the malfunctions, maintenance problems, and poor aesthetics. Users must have a sense of what the technology is capable of before they can grasp how to modify it and apply it to their own purposes. Our first design has therefore focused more on ease of use, reliability, and aesthetics than on minimizing cost.

We have tried to assume a modest availability of technical tools and skills for the end user, and have tried to facilitate assembly by providing very detailed assembly documentation (Figure 2(b)). The builder needs to have a laptop or PC with a USB port, and basic assembly tools including Allen keys, screwdrivers, scissors, pliers, and a soldering iron. Assembly consists of snapping together the acrylic structure, inserting nuts and screws and threaded inserts, bolting together the positioning system components and mounting them to the structure, making cables to connect the microcontroller to the amplifier boards, and the motors to the amplifier boards, mounting the electronic boards to the chassis, and bundling and routing of cables. Soldering and crimping of cables and connectors are the most challenging assembly tasks, but the project documentation is exhaustive, offering advice, images and reference websites for these and almost every other task. The user is expected to have some patience as well: completely assembling a kit from parts to operation requires roughly 18 hours of labor. Currently, the parts cost is estimated to be $2300, including the cost of having acrylic parts laser-cut, and not including shipping costs (remarkably, the Altair 8800 cost adjusted to 2005 dollars would be $2015!). Table I summarizes the hardware parts and costs for the kit.

Table I. Part types and cost breakdown
Table I. Part types and cost breakdown

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Structure

The structural components of our system are built from laser-cut acrylic sheet parts held together with snap-fit joinery and simple “T-nut” style screw/nut fastening, in which a square or hex nut is inserted into a slot in one part, and a screw is threaded in through a hole in a perpendicular part. The tight manufacturing tolerances achievable with laser cut acrylic enable us to produce good orthogonality and alignment in the machine base, increasing the ease of setup and reliability of the machine. Our first three units have been produced in-house with an Epilog Helix 35W laser engraver (Epilog, Inc.), cutting parts directly from SolidWorks (SolidWorks, Inc.) drawing files, which are in turn generated from a SolidWorks 3D CAD model of the complete system. There are 33 acrylic sheet parts in the chassis, plus an additional 7 acrylic parts for the syringe tool. Currently, 5 sheets of 18” X 24” X 0.236” cast acrylic are used to produce the acrylic parts. Cutting the parts for an entire machine requires three hours on our 35W laser cutter. We have arranged contract manufacturing service (Koba Industries, Albuquerque, NM, USA) for these acrylic parts to simplify the purchasing process for end users, and costs for this service will decrease as order volumes increase. An additional benefit to having the structural parts laser-cut is that there is a large installed base of laser cutters/engravers in the sign making, and trophy and gift engraving industries. The custom nature of the work in these industries should make them amenable to kit builder’s approaching them to have parts made. In addition, most laser-cutting equipment used in these industries does not require specialized CAM software – they operate from an application printer driver, so almost any image editing or vector drawing program can be used to design or modify designs for laser cutting and engraving. Thus, modifying the structure of a Fab@Home system does not require an investment in 3D CAD software to make or publish new hardware designs, and the bitmap engraving possible with these laser cutters allows them to customize the appearance of their machine with images and text.

Positioning

The linear motion components of the positioning system use off-the-shelf linear ball-bearing pillow blocks running on ½” diameter rails (McMaster-Carr, Inc.). The X and Y axes are in a gantry configuration with the deposition tool riding on the Y axis, which in turn rides on the X. The Z axis moves the build surface independently from the X and Y to minimize acceleration of parts as they are being fabricated. We have selected HSI Inc. linear stepper motors for our actuators because of their simple design, high resolution, and the semi-custom manufacturing focus of the company which permits specifying precisely the leadscrew and bearing journal dimensions required for our application, simplifying the overall design and assembly. For the X,Y, and Z axes we use NEMA size 14 bipolar motors with rotor-mounted lead screws. External polymer lead nuts are mounted to the axes carriages. In the case of the X axis, a timing belt and pulleys (Stock Drive Products, Inc.) are used to couple a slave leadscrew to the motor leadscrew to achieve symmetrical drive of the gantry. The force, maximum speed, and positioning resolution all depend upon the lead screw threading selected – in this case 15.8 μm travel per full step, a nominal top speed of 25 mm/s (1600 step/s), and a maximum thrust of 120 N.

Material del depósito de herramientas == == Hemos seleccionado una herramienta deposición jeringa para su inclusión en el modelo estándar de 1 de diseño debido a la amplia gama de materiales utilizables con esos instrumentos, y para la intuición de la operación. La estructura de la herramienta de la jeringa (Figura 3 (a)) también está construido con piezas cortadas con láser de acrílico con carpintería de ajustar a presión y T-tuerca de sujeción. Un motor lineal paso a paso los controles de la posición del émbolo de la jeringa. Empleamos como el tamaño NEMA 8 bastidor del motor con un rotor montado tuerca de plomo. El tornillo de avance, que no está cautivo en el motor, tiene 3,2 micras de viaje por paso completo, y el motor puede alcanzar una velocidad máxima de 5,8 mm / s (1800 pasos / s), y un empuje máximo de 90 N. Para la jeringas de 10 cc que utilizamos, esto equivale a un 1,1 cc / s tasa máxima de flujo de volumen, y una jeringa de presión máxima de 460 kPa (67 PSI). La herramienta de la jeringa se ha concebido para permitir 10cc jeringas descartables (EFD, Inc.) para complemento de entrada y salida, y el pistón que se adjunta y rápidamente liberado del husillo de motor para el cambio rápido de los materiales. Una tuerca de metal encaja perfectamente en el interior de los pistones de la jeringa desechable (EFD, Inc.), y un extremo del husillo de motor ha roscado para que coincida con la tuerca. Cuando firmemente roscado en la tuerca, el husillo de impedimento de rotación con el rotor del motor, y por lo tanto el movimiento del rotor se transforma en movimiento lineal. Desenroscando manualmente el husillo de la tuerca permite el intercambio de jeringuillas, independientemente de la forma completa, sin la necesidad de mover o quitar el pistón. Esto facilita la fabricación de múltiples objetos materiales, y conserva los materiales.

thumb | 200px | Figura 3. (a) El diseño estándar, la herramienta única jeringa, impulsado por un motor paso a paso lineal, (b) Una versión de dos jeringas de un laboratorio de ciencias de la vida

También hemos desarrollado una herramienta de doble jeringa (Figura 3 (b)) que permite que dos materiales que se cargan de forma simultánea e independiente de depósito. Como se mencionó antes, las herramientas están atornillados con el sistema de posicionamiento, y son modulares.

Electronics

Personal computers today typically provide several USB connections, but no longer have RS-232 serial ports or parallel ports, though these are still heavily used by robotics and microcontroller hobbyists. As a result, we have opted to support direct USB connection to our Fab@Home Model 1 system, despite the additional development work and (internal) complexity that this entails. We chose to use a microcontroller with an on-chip USB 2.0 peripheral, the Philips LPC-2148 ARM7TDMI (Royal Philips Electronics N.V.). This is a very high performance, 60MHz, flash-memory microcontroller with a wealth of peripheral functions for future expansion, including ADC, DAC, PWM, counter/timers, real-time clock, high-speed GPIO, UARTs, SPI, I2C, not to mention the USB2.0 peripheral. In addition, it has 512kB of flash memory, and 40kB of RAM. The large program memory has enabled us to make a very easily understood and extensible packet data protocol for communication between the PC application and the firmware. We use the large RAM space to buffer motion commands so that real-time motion does not depend on variations in communication bandwidth. With our current protocol, we can buffer roughly 670 6-dimensional path points (for up to 6 axes of control). The microcontroller is powered by the USB, and thus can be communicated with even when the amplifier electronics are not powered. The high computational performance of the device enables the system to handle receiving and buffering path points, sending real-time status and position data, and controlling step and direction outputs for 6 axes at at least 5kHz. The microcontroller is available on a 1.5” X 2.5” board (Figure 4(c)) with header connectors for all pins and a USB connector for $US39.95 in single quantity (LPC-H2148, Olimex, Inc.).

Figure 4. The electronics boards of the Model 1: (a) DB25 to screw terminal breakout board at top center; (b) 4-axis stepper motor amplifier on the far right; (c) LPC-H2148 microcontroller board at bottom left
Figure 4. The electronics boards of the Model 1: (a) DB25 to screw terminal breakout board at top center; (b) 4-axis stepper motor amplifier on the far right; (c) LPC-H2148 microcontroller board at bottom left

Currently, we are using a Xylotex 4-axis stepper motor amplifier board (Figure 4(b)) to power the positioning system and syringe tool stepper motors. This board provides switch-mode current regulation for 4 bipolar stepper motors per board. The current regulation allows us to use a 30W laptop-style 24VDC power supply and 5V rated motors to get much higher acceleration (hence faster builds at finer resolutions), than would be possible at the nominal 5V. This is a design decision which increases cost significantly (relative to using unipolar stepper motors) for the sake of making the technology more useable.

Software

The firmware for the LPC-2148 microcontroller was developed in C language, using Rowley CrossWorks for ARM integrated development environment (IDE) (Rowley Co. UK) which employs the free GNU GCC C/C++ compiler. CrossWorks is not essential - several freeware IDE’s, such as GNUARM exist which work with GNU GCC compiler. The firmware performs the following main functions:

  • receiving and parsing of packetized commands from the PC via the USB
  • buffering of motion path segments for fabrication paths
  • immediate execution of jog motion and emergency stop commands
  • configuration of limit switches (present/absent for each axis and direction)
  • communicating axes positions, limit switch states, and other system status to the PC via the USB
  • controlling step and direction outputs for up to 6 axes at > 5kHz step frequency

As mentioned before, the microcontroller has additional resources available for future expansion, and the firmware has been designed with ease of expansion in mind.

A PC application has been written which enables the user to control the machine, import, position, assign material properties to, and generate and execute manufacturing plans for geometry data which is imported in the form of STL files. In addition, the application has been designed around the concept that while the core application may eventually be improved by the user community, in the short term, the hardware configuration, the types of materials, and parameters for depositing materials would be far simpler and more interesting to explore and share. Thus the hardware configuration, material properties, and material deposition parameters are described in plain text parameter files. These files describe, for instance, the color and geometry data used to render the Fab@Home machine, the speeds and threading of the stepper motors, presence of limit switches, etc.

Figure 5. A screenshot from the PC application displaying a model ready for fabrication and dialog boxes for positioning and real-time status information
Figure 5. A screenshot from the PC application displaying a model ready for fabrication and dialog boxes for positioning and real-time status information

The PC application is currently targeted only for the Microsoft Windows (Microsoft, Inc.) operating system. It is written in C++ using the Microsoft Visual Studio .NET (Microsoft, Inc.) development environment, OpenGL (SGI Inc.) for graphics rendering, and the Microsoft Foundation Class library for user interface components. The application has been designed with the aim of maximizing the intuitiveness of use. The user interface (Figure 5) includes a 3D rendering of a Fab@Home machine which moves synchronously with the real-time position information sent back by the microcontroller. Dialog boxes allow importing and assigning material and tool properties to the part geometry, manual jogging of the axes via buttons and mouse scroll wheel, including the syringe tool motor, as well as a numerical view of the real-time position and status data from the microcontroller. The application also allows a rudimentary simulation of the fabrication process – the actual manufacturing plan is executed on a Fab@Home software emulator, and the motions are displayed in the GUI for quick checking of toolpaths.

The workflow for Fab@Home consists of the following:

  • connecting PC to Model 1 via USB cable, and plugging in the Model 1’s power supply
  • selecting and/or modifying/tuning parameter files to match the hardware and materials to be used
  • starting the PC application
  • loading the parameter files
  • loading a syringe with piston, material, and nozzle, and mounting it in the tool; threading the tool leadscrew into the piston nut
  • importing the geometry of the part to be fabricated
  • assigning material and tool properties to part geometry
  • automatic generation of a manufacturing plan
  • if desired, simulated execution of the plan
  • establishing communications with the Model 1
  • homing of the axes so that GUI and physical positions match
  • jogging axes to the desired origin for fabrication
  • automatic execution of the manufacturing plan

Building a Model 1

To build and use a Model 1, you will need to do the following:

  1. Buy tools required for assembly
  2. Choose your style options
  3. Buy the parts for the Model 1
  4. Build the cables and subassemblies
    1. Cables
    2. Machine Base
    3. XY-Carriage
    4. Z-Carriage
    5. 1-Syringe Tool
  5. Assemble the subassemblies into the complete Model 1 System
    1. Assembling the Chassis
    2. Mounting the 1-Syringe Tool
    3. Preparing and mounting electronics
  6. Program the LPC-H2148 with the Model 1 Firmware
  7. Install the Fab@Home Model 1 Application
  8. Commission the Model 1
  9. Use the Model 1

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