How the DLP 3D Printer Reference Design Works
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1.3.5 Mechanical Structure
The DLP 3D Printer mechanical assembly is constructed from 0.25" thick aluminum plates to make the
structure as rigid as possible. The structure's role is to hold the orientation of the build platform/translation
stage, photo-resin vat, and projector tightly, in relation to each other, to reduce dimensional errors in the
printed objects. The mechanical assembly features an easily removable photo-resin vat.
1.3.6
DLP 3D Printer Microcontroller
The DLP 3D Printer has to synchronize motor control along with exposure of the object layers, as well as
supply an interface with a front panel LCD screen and user buttons. An MSP430F2410 controls the
operation of the DLP 3D Printer onboard a stand-alone capable BeagleBone Black MSTP Cape. The
MSTP cape contains the microcontroller and a DRV8825 stepper motor control IC. The
MSP430/DRV8825 combination is capable of driving bipolar and unipolar stepper motors with phase
voltages between 8.2 V to 45 V. The DRV8825 can output up to 2.5 A of current at 24 V. The MSTP cape
must be modified by the addition of connections between the microcontroller and header pins. The
connections that must be added are highlighted in red in the cape schematic in the TIDA-00293 design file
package.
1.3.7 Front Panel User Interface
Users can interface with the DLP 3D Printer through a front panel once the print has been started. A 4-line
LCD screen with 20 characters per line displays information to the user such as the number of print layers
and the current layer in the print sequence. The LCD screen is controlled by the MSP430 through an
HD44780 controller. The front panel also has two buttons allowing users to interact with the printer, either
by responding to LCD prompts or pausing -- and even cancelling -- the print sequence.
1.3.8
DLP 3D Printer Graphical User Interface
Object layer images are uploaded to the DLP 3D Printer hardware utilizing a GUI. Object layer images
must be 912 × 1140 resolution due to the native resolution of the LightCrafter 4500. The images are
processed by the DLP Structured Light SDK into a firmware file containing the sequence of layer images.
The GUI takes a basic set of parameters from the user including: LED current setting, layer exposure time,
z-layer step resolution, resin settling time, and the directory where object layer images are kept.
1.3.9 Object Layer Images
Object layer images can be made by hand using a drawing utility, or created by slicing STL file models.
STL files are the de facto standard input file for 3D printers, and are readily available in multiple online
libraries. STL files can be sliced using the Freesteel slicer utility found here:
http://www.freesteel.co.uk/wpblog/slicer/
. The output image file format recommended is BMP. The output
images should have a 16:10 aspect ratio as output from the slicer, but be resized to 912 × 1140. Resizing
the images will change the aspect ratio, but the diamond array of the DLP4500 DMD will return the image
to the proper 16:10 aspect ratio once projected. Object features should be colored white and the
background should be black. Any white pixels in the object layer images will be printed in the resin.
The object layer images must be isolated in a file directory and stored in alpha-numeric order. Freesteel
slicer will handle this for the user if a static output file name is supplied. No other files should be kept in
the directory with the layer images.
8
Introduction to the DLP
®
3D Printer Reference Design
DLPU025 – September 2014
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