KSA FAB LAB > Microscribe

3D Digitizing Arm Tutorial

Wednesday, January 26th 2005
Category: Fab Lab

This tutorial describes how to connect to and use the school's 3D Digitizing Arm.

The school's digitizing arm consists of two physical components: the arm, and a set of foot pedals. The arm and pedals are located in the school's Fab Lab, in room 50D of Knowlton Hall.

To use the arm, position the object you wish to scan on the desk, such that the arm can easily reach the farthest point of the object. If your object is too large, you will need to re-calibrate the arm each time you move either the object or the base of the digitizing arm.

In this tutorial, we'll be digitizing the object at right - a crumpled piece of paper. The grid that has been drawn on the paper will help us, by ensuring that we evenly cover the object's area.

For some objects, a single grid will not be sufficient to accurately translate the object into FormZ. In that case multiple grids can be used, but you will need to stitch the separate objects together into one object using FormZ (or another modeler, if you are more comfortable with another package).

Step 1:
When you are ready to begin digitizing, be sure that the digitizer is powered on (there is a power switch on the back of the base, and a green LED light on the base to indicate that it is turned on) and load FormZ.

Step 2:
The next step is to set up the digitizing arm. This can be done by opening the "Extensions" menu, and choosing "Microscribe Digitizer" item and "Microscribe Setup..." as pictured at right.

The default settings are pictured at right. You can change the Baud rate if you'd like - any speed should allow accurate communication. The snap tolerance can also be adjusted to suit your preferences.

Click "OK" when you have adjusted the settings to your preferences, and FormZ should return to the main interface.

If, during any of these steps, you get an error message indicating that the digitizing arm cannot be found, double-check all of the cable connections going into the arm and into the CPU below the desk. The IT Staff has seen problems occur when any of the connections are loose - resulting in the computer not being able to communicate with the digitizing arm. As a last resort, you can also try rebooting the computer completely to restore your connection to the digitizing arm.

If you are still unable to connect to the arm, please file a Problem Report Form, and we will troubleshoot the equipment from there.

Step 3:
The next step is to calibrate the digitizer. This allows FormZ and the Digitizer to establish a common frame of reference, allowing you to translate geometry from the real world into the computer model.

You start the calibration process by opening the "Options" menu, and selecting "World Digitizer Calibration..."

At this point, the following popup window will appear. You can use any of the calibration methods, but this tutorial will describe the "3 points" method.

Click "OK" when you have selected the calibration method you wish to use.

Please Note: From this point forward, you must be careful not to move either the base of the digitizing arm, or the object you are digitizing. Doing so will require you to start over from this point!

FormZ will now ask you to identify three points using the digitizing arm. Illustrated at right are the three points used in this demonstration.

You select a point by placing the stylus on that point, and stepping on the right digitizing pedal once. Move the stylus to the second point, step on the pedal again, and repeat the process for the third point.

Any three points can be used - but you should remember which points you used. You should also be able to specify where in the digital model those points exist.

These three points form a triangle, with point 1 at the intersection of a right angle.

After you have specified the three real-world points, you will be asked to identify the same three points within the FormZ model. Use the mouse for this operation, left-clicking to identify each point.

The image at right shows the three points used in this example. Please note that these three points have the same relationship among themselves as the points used in the preceding step (the three points form a triangle, with point 1 at the intersection of a right angle).

Step 4:
The calibration process is now complete, and you are ready to start digitizing your model!

To start digitizing, choose "World Digitizer Input" from the "Options" menu, as shown at right. You can also turn digitizer input on by pressing the F3 key at the top of your keyboard.

If you are inputting a mesh, you can also turn on mesh input with the "Capture Digitizer Mesh" command, also shown in this image. Regardless of whether you are creating a mesh, however, the "World Digitizer Input" option must be selected.

Please Note: While you have the digitizer input mode active, you will be unable to change any tool settings in FormZ, or use the interactive pan/zoom features of the view menu. For this reason, we recommend that you set all tool settings and your view before starting to digitize any object.

At this point, start digitizing by placing the stylus on your first point, and enter that point by stepping on the right pedal once. Move the stylus to your next point in that row, step on the right pedal again, and repeat until you reach the end of that row.

When you reach the last point in a row, close that input row by stepping once on the left pedal. This will simulatneously digitize that point, and close the row. You are then free to repeat the process for the next row of your grid, continuing through all rows until you have finished digitizing that mesh.

After finishing that mesh, turn off "World Digitizer Input" (either by pressing the F3 key again, or by opening the "Options" menu and clicking on "World Digitizer Input". If you were using the "Capture Digitizer Mesh" option, FormZ will now give you the choice of what options to use to create the mesh. Choose the options you desire, and click "OK" to create the mesh.

Voila! You're done using the digitizer. If you have other meshes to digitize, you can repeat this process as many times as necessary. If, during this process, you need to move either your object or the base of the digitizing arm, you will need to re-calibrate it, starting with Step 3 of this tutorial.

Hopefully this tutorial has proved helpful. If you have any questions about the steps outlined here, please contact the IT Staff for assistance.

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