TRap

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Revision as of 22:58, 4 September 2010 by Mccand (talk | contribs) (Concept 1: Modified Delta Style Manipulator)
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TRap

Release status: unknown

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Description
Documentation of TRap development
License
Author
Contributors
Based-on
Categories
CAD Models
External Link

The TRap will be an alternate mechanical structure for the reprap project. Team TRap intends to make it an entry in the Kartik M. Gada Personal Manufacturing Prize. Before I go any further, I want to thank Team Columbus: I have used Isaac's basic layout for this page.

Overview

The Gada Prize

The main requirements of the Gada Prize are:

  1. Print at least three different materials, including one that is usefully electrically conductive.
  2. Demonstrate the ability to print electronic circuit boards.
  3. Any print beds must be of a material which may be reused with minimal refurbishment for at least 20 print cycles.
  4. Maintain a total materials and parts cost under $200.
  5. 90% of the volume of the device's components shall be printed.
  6. Demonstrate a build volume greater than 300mm[11.81in] x 300mm[11.81in] x 100mm[3.94in].
  7. The capacity to print a full set of components for a complete replica of itself within 10 days unattended save for clearing no more than one printer head jam.
  8. The ability to print autonomously without a PC attached.
  9. Uses no more than 60 watts of electrical power.

Current Status

I am currently brainstorming various ideas and configurations for use in the TRap.

Current Challenges

  • I need a couple of team members. I could use a builder and a control person/programmer, but I don't think I'd turn down help from any interested party.

TRap Specifications

The table below outlines the specifications of the machine.

Metric[Imperial]
Manufacturer Anyone
Model TRap
Technology FFF (Fused Filament Fabrication)/Thermoplastic extrusion
Price of all materials TBD
Annual Service Cost TBD
Size 400mm[15.75in] x 400mm[15.75in] x TBDmm[TBDin]
Weight TBDkg[TBDlbs]
Build Envelope 300mm[11.81in] x 300mm[11.81in] x TBDmm[TBDin]
Materials TBD
Material Cost TBD
Speed TBD
Accuracy TBD
Finish TBD
Volume of printed parts to replicate TBD

Concepts

Concept 1: Modified Delta Style Manipulator

TRap Concept 1: Structural sketch.

See Workbook entry for September 03. This system is based on "Delta" pick and place robots, but some modifications have been made: the servos are used in prismatic joints, rather than revolute ones. This allows for much more precision (perhaps too much) at the cost of speed. The exact trade-off can be sdjusted by altering the tetrahedron design, the axis design, and several other variables. A second variation from "traditional designs" is the use of the tetrahedra to move the servos as low as possible in the design. This eliminates the need for extensive superstructure.

A point of note: I am not the first person to try to design a delta style reprap. I spent some time poking around on the internet to find any prior art, and it looks like Helium Frog and Viktor, and reinoud70 have built WORKING versions before I even started to imagine the possibilities. A few thoughts: All of these models use extensive support structures that enclose the build envelope, and use some parts of which are much larger than the available build envelope. I hope to avoid this with my design. (While the base plate is large, it will be able to be assembled in pieces, and needs only a flat surface to rest on.) What they have all done, that I am really worried about needing to do myself, is figure out control schemes! Good work! I hope I can do as well.

Concept 2: Pyramidal Pendulum Manipulator

This was loaded into the workbook on September 04. At this point, I do not have a good structural sketch, just a poor pencil drawing. (Sorry!) This concept has two major issues: First the extruder platform tilts during use. While this can probably be corrected with clever use of extra arms and universal joints (something like a parallelogram 4-bar linkage), I still need to work out the details. The second problem is that this design requires more extensive structure, including parts that are longer than the build envelope. This means purchased parts, which cut into both my budget and percentage of printed parts. Currently I think that Concept 1 addresses both these issues adequately. All that said, this design has an advantage in that it requires a relatively small volume of printed parts, and is scalable simply by lengthening the axes and legs!

Provenance: I have not done any research yet to see if others have already pursued this idea. If you (the reader) knows of something, please let me know!

Concept 3: Prismatic Axis

Concept 4: Reprap-able Universal Joint for Delta-Style Manipulator

Design Philosophy

  1. The TRap will make use of a parallel manipulator
  2. The number of unique parts shall be kept to a minimum
  3. Parts shall be made as simple as possible
  4. Identical parts will be used wherever possible
  5. Orthogonality shall be preserved wherever possible
  6. Non printed parts shall be "Off-the-Shelf" (OTS) whenever possible
  7. Modifications to OTS parts should be avoided wherever possible.
  8. Substitution of similar OTS parts should require a minimum number of changes to the design (i.e. a change of bearing size)

Nomenclature

Key Concepts

  • Parallel Manipulator

Structure

  • Concept 1 is out! see work log below.

Print Bed

Axes

  • 3 Identical Axes assemblies

Extruder

  • TBD, possibly Bowden due to the light weight.
  • Eventually, a three material extruder needs to be developed.

Control Systems

  • TBD, this will not be a trivial problem

Workbook

2010 September 01

  • Registered team on the RepRap wiki
  • Started concept generation

2010 September 02

  • Created this wiki page; thanks again to Team Columbus, who provided the format.

2010 September 03

  • Finished mocking up Concept 1.
TRap Concept 1: Structural sketch.

This is worth taking some time to explain. TRap is a manipulator with a parallel kinematic chain. I am using a variation on the normal Delta robot design that is most often seen in "Pick-and-place" robots. This design approach has two major advantages: it can be very fast, as the arms manipulator platform has a very low intertia (servos are all stationary); and all three axes are totally identical, reducing part count. The major disadvantage is that the control problem is not trivial: getting the end effector to move with constant velocity along a straight line involves all three servos.

The major parts of this design are:

  1. Base Plate: This is easily the largest part, and will have to be split into several different (preferably identical) parts to be printable. In this concept, the build surface is not part of the baseplate, but can be places on top or, or underneath the base plate. This will probably change as the design is fleshed out more.
  2. Motorized axes: These are shown much simplified (no motor), and the details still need to be worked out. The gist of it is that they will pivot around their attachment to the base plate, and they will act to move one vertex of a tetrahedron.
  3. Tetrahedra: This is merely a force redirecting structure. It allows me to have much less structure than some other tripod designs. Three are required.
  4. Arms: A length of printed plastic with a universal joint at each end. Six are required.
  5. Platform: This is where the extruder will live. One required.

Note: The blue lines on the sketch show the desired working envelope. As yet, things still need to be scaled a bit to avoid mechanical singularities.

2010 September 04

  • Uploaded Pyramidal Pendulum Manipulator concept sketch
  • Uploaded Universal joint concept sketch
  • Uploaded Axis concept sketch
  • Created Concept section on main page

General Notes

In accordance with the official Gada Prize rules regarding documentation and transparency - as interpreted by the RepRap Core Team and others - all documentation for this project will take place here in this wiki. If there happen to be any "Other Spaces" out there that have documentation for this project, then such information is posted there only after it is posted here.

  • The following notes help to keep this workbook in a neat and orderly condition and shall be generally adhered to throughout all levels of documentation.
  1. All dimension and temperature nomenclature shall include both SI and Imperial units. SI units shall be first followed by Imperial units in brackets. Examples: 100mm[3.94in] and 40°C[104°F]