GeoTracer Scanning

GeoTracer is one member of the Geomet Suite of Reverse Engineering Tools. GeoTracer is designed to capture large amounts of data points using a hard ball probe by dragging the probe over a surface expanding the usefulness of your manual Coordinate Measuring Machine.

When activating the GeoTracer tool, you will be presented with a parameter dialog which you set the performance characteristics, see figure 1.

figure 1, GeoTracer Parameters

The value entered becomes the length Geomet will use to establish the minimum distance between data points. When GeoTracer is in motion, the CMM sends a constant stream of data points to Geomet. The first data point captured will be stored and all incoming data points will be compared to the first point until the distance between points exceeds the target distance. Once that minimum distance has been met, the second point will be captured and the process repeats itself.

The value entered here will limit the size of a single data cloud that is stored as a single feature. Once the data cloud size equals this value, Geomet will create a new feature in the inspection report that contains the captured data points. Geomet will then recycle the GeoTracer allowing you to continue capturing data without stopping. The purpose of limiting your data cloud size is only for convenience to limit how much data will be included in one feature.

When you compete the GeoTracer parameter dialog, you will be prompted to capture data points, see figure 2.

figure 2, GeoTracer Prompt

Once the prompt appears, the capturing of the data points is suspended allowing you time to move the CMM into position on your part. This is indicated by the Probe Disabled statement next to the Current Status prompt.

When you are ready to capture data, press the space bar, or depress the optional foot switch. Geomet will capturing data when you start moving your probe across the part. Pressing the space bar again will cause Geomet to return to a Disabled Probe state and create a feature based on the captured data point count.

The GeoTracer tool can be used on DCC style CMMs as long as you can disable the motion drive system. To disable the motion drive system within Geomet, activate the System Options <F9>, see figure 3.

figure 3, Activate DCC Commands

As shown in figure 3, the setting "Activate the DCC commands" is highlighted. Change the setting to 'No' and press <Ok>. You can now change your probe system by installing the hard probe to be used by GeoTracer and follow the GeoTracer instructions.

The data points being captured will be the XYZ location of the probe ball center. Since probes do not offer vector feedback informing the host measuring software where the contact point was on the ball, a determination of surface points is not possible. This condition can be corrected by exporting the data clouds to most of the popular CAD systems and then constructing a surface followed by offsetting a surface by the probe radius.

If your intent is to take the data clouds and export them to a CAD system, it is helpful to organize how you capture the data clouds. Most manual CMMs offer locking mechanisms on the X, Y and Z-axes. This allows you to lock one axis and drag the probe over your part to form a single line of data points. When you reach the end of your captured data point line, press the <space bar>, this will create a feature in the inspection report. Next, remove the lock and move to a new location and reset the lock repeating the drag operation to create a parallel set of data points.

The Cardinal Spline tool will create a fitted spline through your data points which offer a smoother transition for the CAD system to fit a surface to the data points you captured. See Cardinal Spline for detailed usage.

The quality of the data points can be affected by the speed of the CMM while capturing the data points. A CMM interface captures the XYZ scale values based on a timed cycle. Some interfaces cycle 30 times or more per second, such as the Helmel ProCounter series. At this cycle speed you will capture a consistent set of data points while dragging your hard probe at normal speeds between 2" (51mm) and 5" (127mm) per second which translates to capturing approximately 20-50 points per second.

If your CMM interface cycles at a lower rate, such as most interfaces on Direct Computer Control (DCC) CMMs, the cycle can be slowed down to as little as 3 cycles per second. On this style CMM the actual reading of the XYZ scales is performed by the motion controller and forwarded to the host measuring software as a status update. At the slower cycle rate, the drag speed required to produce a uniform set of data points must be reduced to speeds around 1" (25mm) per second.

Should the drag speed to fast the spread between data points will be greater than the requested distance set in the GeoTracer Parameters. If you find undesirable results in the spread of your data points, slow down the drag speed.

Related Procedures:

Cardinal Spline, Select Scan Method, 4-Point Boundary Scan, Radial Boundary Scan, Line Scan, Export Tool