Using auto direction on 1D Points can lead to erroneous reported values if used incorrectly. Auto direction relies on a smooth approach, from you the operator, in capturing of a data point. The process of determining the approach vector involves the CMM interface card (ProCounter, Tech 80 or PMAC) to maintain a rolling IJK vector based on the last five reported values. These interface cards update the current position in the MCS on a programmable time interval from 20 to 200 milliseconds.

figure 1, Auto Direction Approach Vector

When you are approaching your work piece, it is required that you make contact while remaining in a ±45° approach, see figure 1. In this example, if we remained in the approach zone we will capture a data point that will be reported as a +Y point. If the operator did not remain in the approach zone the 1D Point might report a + or - X Point from which we will have to correct the probe compensation error. Most common occurrence of a erroneous data point comes from operators who approach the surface, and then pause during the approach and attempt to make contact under extremely slow speeds, which while approaching causes variations in the path toward the surface.

Switching Reported Axis on 1 Points

figure 2, 1D Point Correction

To correct the reported direction of a 1D Point, highlight the feature by left-clicking on it, then right-click to bring up the feature menu, as shown in figure 2. Select [Point Direction] which will offer a sub-menu with all six probing directions available. Choose the correct 1D Point direction and your part inspection will update with the correct 1D Point. Note: Once a feature has been referenced it can not be changed or edited. For example, if a feature was used in the construction of a PCS , it will be locked from changes. This is identified by the inclusion of a ¹ next to the feature number, example " 12¹ ".

Using Auto-Direction with multi-point features such as circle, lines and planes can also incorrectly report feature characteristics. This occurs when capturing data points in an inconsistent method or by capturing data points at a high rate. As previously mentioned, the calculation of the direction vector for the probe works off the speed of the interface and should that rate of point capture be to high, the changes in direction going toward, then backing off the data point will create a poor direction vector.

Since touch probes can be effected by speed and our auto-direction tool is also adversely effected by speed, we suggest the use of a smooth consistent approach speed and rate when capturing data points.

Activate Auto Direction Sensing

To activate the Auto Direction sensing go to System Options, <F9> and locate the Auto Direction sensing key.

To activate, change the choice to 'Yes' next to the Auto Direction sensing key.

During the inspection process you may require to control the Auto Direction sensing manually. This can be accomplished through the Feature Measurement Toolbar or by pressing the <u> key on the keyboard. The iconic button on the toolbar will indicate the status of the sensing option. In figure 4, the button shows an "X" through the button. This indicates that if the button was pressed, you will take sensing off.

figure 4, Auto Direction is ON.

In figure 5, we see the iconic button shows no "X" over it indicating that if you press the button, it will turn the sensing back on.

figure 5, Auto Direction is OFF

Although the visual appearance of these iconic button appears to be backward it actually represents what the button will do should it be pressed. The button is not designed to represent the current state of the Auto Direction Sensing.