Method of using a support structure as a fiducial for measuring position

A method of building a three-dimensional part in an extrusion-based additive manufacturing system, the method comprising the steps of:

• extruding build material from one or more print heads in a planar X-Y layer supported on a platen to print a layer of a three-dimensional part and a layer of a fiducial structure, the fiducial structure having a substantially vertical surface and a substantially horizontal surface;
• determining a known X-Y location of the fiducial by measuring the substantially vertical surface and the substantially horizontal surface of the fiducial structure in the planar X-Y layer;
• determining a Z location of the three-dimensional part by locating a surface of the printed layer of the three-dimensional item;
• incrementing the platen along a Z-axis to increase the distance between the platen and the one or more print heads, so that the one or more print heads are positioned to extrude build material in a subsequent planer X-Y layer;
• determining a subsequent known X-Y location of the fiducial by measuring the substantially vertical surface and the substantially horizontal surface of the fiducial structure in the subsequent planar X-Y layer;
• determining a subsequent Z location of the three-dimensional item by locating a surface of a last printed layer of the three-dimensional item
• comparing the determined subsequent X, Y and Z locations to the X, Y and Z locations determined before incrementing the platen and calculating a shift amount when a discrepancy exists;
• and
• shifting the one or more print heads by the shift amount when a discrepancy exists;
• and
• printing one or more additional layers of the three-dimensional item and the fiducial structure.

A method of building a three-dimensional part in an extrusion-based additive manufacturing system, the method comprising:

• printing a support structure for the three-dimensional part in a layer by layer manner along a printing axis, wherein the support structure has a fiducial structure having a known substantially vertical surface and a known substantially horizontal surface;
• printing one or more layers of the three-dimensional part along the printing axis while supporting the three-dimensional part with the support structure;
• moving the printed support structure and the printed portion of the three-dimensional part along the printing axis a distance;
• locating an X-Y position of the fiducial structure by probing the known substantially horizontal surface of the fiducial structure to determine an X position, and probing the known substantially vertical surface of the fiducial structure to determine a Y position;
• comparing the located X-Y position of the fiducial structure to a previous located position of the fiducial structure to calculate a measured X-Y offset;
• compensating system parameters to remove the measured X-Y offset;
• and
• printing one or more additional layers of the support structure and the three-dimensional part onto the previously printed support structure and the portion of the three-dimensional part.