PWI000042
this document applies to :
Gripe no 389
PowerINSPECT can support a wide range of measuring machines and probe types. Trigger probes are fitted to most conventional CMMs. This note describes measurement technique using trigger probes.
Trigger probes send point data ('trigger') automatically on contact with a surface- the user does not have to use any other controls to take points.
During guided measures the user must bring the probe into contact with the surface in the desired region. The easiest way to do this is to concentrate on one axis at a time, locking the axes if this function is available. When the positioning is correct in two axes, the probe can be moved along the third axis until it touches the surface.
This technical note describes measurement of 'guided' features with Trigger probes. The common characteristic of 'guided' features is that the probe must be positioned in a carefully defined area, or else points will simply not be taken. A typical example is a section. Points for section measurement can only be taken within the tolerance zone either side of a previously defined plane. If the probe is outside this area points will not be taken at all.
Trigger probes send point data ('trigger') automatically on contact with a surface- the user does not have to use any other controls to send points. In guided measures, points will be taken only if the probe is in the correct position when it is brought into contact with the surface.
During guided measures you have to strike the probe gently against the surface in a specified position. The easiest way to do this is to position the probe near to the surface and near to the required point. The ideal is to position the probe very close to the surface along the normal that runs through the guided point. When you move the probe directly towards the surface it will contact with the surface in the required position.
In practice, it is often easier to move the probe perpendicular to your surroundings rather than perpendicular to the surface. For example, it is easy to guide the probe vertically, or to your left or right, or along the axes of a CMM. If you choose to do this you should ensure that the direction you use for the approach is the one most perpendicular to the surface.
This technique can be helped by the use of axis stops if these are available. These allow you to fix the probe in one axis at a time (usually the X,Y,Z of the machine coordinates), allowing you to determine the correct position one step at a time.
To take a point with a device using a trigger probe, simply bring the probe into contact with the part. The contact will trigger the probe. This is all that is required.
This section describes how to measure a guided point using a trigger probe, but the same technique applies to sections.
Guided points are used when a surface measurement is required at a pre-defined location. The aim here is to bring the probe in contact with the surface at a pre-determined point. Guided points are described in the User Guide under 'Using Guided Points' in the 'Inspecting Surfaces' chapter.
When you take points you can monitor your progress in two ways. If tracking is supported on your system, you will see a representation of the probe on the screen- the aim here is to put the probe contact point on the surface of the model at the centre of the target.
You can also use the progress bar at the bottom of the Guided Points dialog box. When you take a point on the part, PowerINSPECT shows how close you are to the point using the progress bar. The closer to the target point you are, the more the progress bar is complete.
When you are at the target point, the point is recorded and its measurement results are displayed on the right of the Guided Points dialog box.
If you are taking a number of points, the next target will appear at this stage. Please note that you can only take more than one guided point at a time if they are have not been previously measured. This occurs in two cases: firstly, if you have imported the guided point targets either from a file or copied them from dynamic points; secondly, if you have used 'Measures - Add New Measure' to repeat an inspection on a different part of the same design.
When you have finished taking points, click on the 'tick' button to finish measuring, and the points and results will be shown in the CAD view.
