Rapid Prototyping Technique for Designing Joints Using Bezier Curves.

Rapid Prototyping technique for designing
articulated, interleaved or intercalated joints
using Bezier curves in modeling
complex robotic movements

R. Siderits MD
P. Clifford MSIV
J. Hawkins DO
M. Swift Exp-Path Team
K. Cannon MSII Exp-Path Team
V. Singh EXP-Path Team

Step 1: Examples:

Here are several examples of Laser cut parts designed using the Bezier curve technique.

interlock1.avi
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Step 2: Technical Brief:

It is often necessary when developing components for automated systems to designing complex sequenced movements which use irregularly shaped parts.

There is also the challenge of designing this part quickly and reproducibly in a way that allows for redesign for on the fly prototyping. For example you may need to create a simplified endoskeleton with a freeform 2D joint for a robotic manipulator that has a limited range of rotation about a user defined axis and framed detend points.

The joint needs to be either interleaved (something goes between something else, like a leaf in a table) Interlocking (something happens before or after something else in a sequence of movements) or intercalated (something happens during an action).

Step 3: Overview:

We describe a rapid method for design and fabrication of prototypical interleaved, interlocking or intercalated joints with a Bezier trace-contour approach to developing paths for prototyping movements of parts prior to fabrication. We use a CAD or Graphics program and a laser cutter to create parts from hand drawings (Art-to-Part) and free-form CAD designs of complex movement (Notion-to-Motion) within minutes.Advantages to this approach include the following:

1) ease of use
2) ability to use scanned hand drawings in rapidly configuring part contours
3) the ability to define limiting contours for path-tracking
4) design iterations by reloading and modifying the CAD/graphics program
5) parts can be scaled up or down as needed,
6) rendering the scene with atmospherics for manufacturing proposals
7) annotating parts with logos or assembly text
8) arrayed cutting and serialization for part production.
9) Path following for developing tracked movement with oscillation.

Step 4: Basic Approach - Part I:

1) Open a graphics program that can draw lines using a Bezier curve.

2) Create the outline of the part and close the path.

3) Alter the contour of the part by dragging the controls and points that define the Bezier curves.

4) Select a center of rotation for the part.

5) Copy the part, paste down a copy of the part and rotate it a few degrees about its center of rotation.

6) Repeat until the full range of desired motion is portrayed by the copied parts.

Step 5: Basic Approach - Part II:

7) Place fixation and pivot points for drilling

8) To create an outter surface for the enclosed joint; create a copy of the limiting contour and paste it down, then delete a few points in the Bezier near the front of the joint. Remember to make a front and back.

9) View the parts from a Top down view and render the image in black and white.

10) Bring the image into the Laser program and use a Trace to outline the parts.

11) Delete the background image and cut the outlines.

Step 6: Hisotrical Note: Who Was Bezier?

Give a general description of the StepPierre Etienne Bezier was born on September 1, 1910 in Paris France and was a great mathematician and engineer. He is known today as one the founding fathers of computer-aided design and computer graphics systems because of his initial work with three-dimension free form structures such as the Bezier curves and Bezier surfaces. Pierre received degrees in mechanical engineering from the Ecole des Arts et Metiers and in electrical engineering from the L'ecole Superieure d'Electricite in 1930 and 1931 respectively. In 1977 he was awarded the Doctor of Science from the University of Paris. At the age of 23, he went to work for Renault, his research interest was creating and developing UNISURF one of the first CAD CAM model systems for car body design.

Step 7: Final Step: Cutting the Parts

We use the Pinnacle V-series laser cutter/engraver. This system will cut and engrave without user input or lens changes. The 30W version will cut up to 1/4 inch Plexiglass.
Using the accompanying Pinnacle V-Series software, we imported the black and white overhead or Top view image that was generated by trueSpace CAD program and selected the Autotrace function. We deleted the area outlined by the autotrace so that only the traced outline remained.

We then selected Contour cut and assigned the outline color (usually red by convention) to a laser power setting and speed that will worked well on the material and thickness that we were using. You may add a logo on the part using the Pinnacle software and "LAZ" it in onto the surface of the part.

A logo or possibly assembly text (part ID) will be assigned a different color outline and will be given a lower power setting and faster speed so that it will engrave the text or image into the part surface and not cut all the way through the material. Next, send it to the laser and within minutes the parts are ready to assemble. It is also possible to automatically "serialize" the parts and then array the laser job to make multiple identical part sets from different materials (including compressed paper or gasket materials).

Step 8: In Summary:

In this Instructable we describe a method for rapid design and fabrication of prototypical interleaved, interlocking or intercalated joints with a trace contour approach to developing tracked paths and for developing complex interrelated movements of parts in systems with automated movement. We use a CAD program and laser cutter to take drawings to parts (art to part) or freeform design of complex movement (notion to motion) in a few minutes. The process described above lends itself to rapid evaluation of joint design features for robotic systems.

Advantages to this approach include ease of use, the ability to use scanned hand drawings to configure part contours, the capability to define limiting contours for path-tracking, reloading CAD scenes at any time to revise part contours to suit system design modifications, parts can be scaled up or down as needed, rendering the scene with atmospherics for manufacturing proposals and concept presentations, annotating parts with logos or assembly text and the use of arrayed cutting and serialization for part production.

Step 9: Discussion and Anecdotal Observations:

What if you don't have a laser cutter?

- The same approach can generate outlines to be cut on with a scroll saw or even a V-Block and coping saw.

- You can model tracked movements by drawing the path then using the same approach.

- Creating an oscillating path using the same approach is also easy as is circular oscillation.

- FREE: graphics program - GIMP http://www.gimp.org

- FREE CAD program - Blender: http://www.blender.org

- Pinnalce V-Series Laser cutter/engraver: http://www.signwarehouse.com/engravers/pinnacle_v.htm

Step 10: Disclaimer:

Follow all safety guidelines, including but not limited to:

1) Using Laser systems or CNC machinery.

2) Powertools that you never read the instructions for.

3) All tools that you never learned to use properly.

4) Anything that heats up, pinches, cuts, squeezes or causes traumatic, caustic or thermal injury.

- We are sharing our experience, not telling you to do it.

- If you choose to try this then - it is at your own risk!

- No really, we're not kidding about this.

Step 11: Project Identification:

Facility: RWJUHH Investigational Pathology Division and Center for Parabiotics Research

Section: Special Projects

Application: Modeling and prototyping complex movement in robotic systems.

Technique: Rapid Prototyping in laboratory development

Title: Rapid design and prototyping of articulated components with interlocking, interleaved or intercalated joints for complex movement in robotic systems.