Probe Type; trigger probes cf rigid probes

PowerINSPECT, Probe Type and Measurement Technique

PWI000041

Context

this document applies to :

PowerINSPECT All Versions

Summary

PowerINSPECT can support a wide range of measuring machines and probe types.

Trigger probes (as fitted to most conventional CMMs) and rigid probes (as typically fitted to articulating arms) require different support from the CMM driver, and also require different measurement technique.

This technical note highlights the differences between trigger probes and rigid probes. PWI000042 describes trigger probe measurement technique in more detail, while PWI000043 describes rigid probe technique.

Description

There are three main issues affected by the type of probe.

1. How the probe is calibrated

2. How points are taken

3. How 'guided measures' (such as sections or guided points) must be handled.

Probe Calibration

In general, rigid probes are calibrated outside PowerINSPECT, and touch-trigger probes are calibrated within PowerINSPECT.

Taking Points with the Measuring Device

It is important for PowerINSPECT to receive enough information to be able to compensate correctly for the probe diameter. This is described in the User Guide's Introduction (How PowerINSPECT Records Points.)

Touch-trigger probes and rigid probes are different in this respect:

When a touch-trigger probe is deflected, the necessary information is produced automatically.
With a rigid probe, the user must point the main axis of the probe towards the material while points are being taken. Failure to do this may result in invalid measurements.

Taking Guided Measures

Touch trigger probes trigger on contact with the part and the aim is to touch the part only at the required location. If the required accuracy is high, repeated attempts may be necessary to achieve this. This is made easier if you look at the co-ordinates for the guided point and move the probe so that it is correctly positioned in one of the axes. Lock that axis on the CMM, then probe the guided point.

Rigid probes are triggered remotely, usually by a separate button, and the best technique is to trigger the probe constantly while crossing repeatedly over the required point. When you are on the target, PowerINSPECT will automatically register the point. Some devices emit a tone while you trigger the probe: the closer you are to the guided point the higher the pitch of the tone.