Modes of operation
Qualification (calibration of the probe)
The SP80 and SP80H probes require qualification (calibration) before it is able to give accurate positional data.
After the probe and stylus combination is calibrated it can be used in a variety of ways. Principally these will be as either a single point measurement probe or a profile measurement-scanning probe. Please refer to the modes below.
SP80 and SP80H can be used as a continuous deflection contact scanning probe for profile measurement or for surface digitising purposes. In this case the CMM controller must respond to the deflections of the probe in real time to maintain surface contact.
Single point measurement mode
The following are methods that can be used for taking single point measurements using a calibrated SP80 or SP80H. OEMs are advised to evaluate each of these to determine the best solution for their own system.
Static averaging method
SP80 and SP80H can be used to take single points to give increased accuracy whilst reducing the effects of machine vibration by performing static averaging.
The probe stylus should be made to contact the workpiece and deflect the stylus to the recommended amount (50 μm). The CMM should be halted and kept nominally stationary.
Whilst the machine is stationary, surface position readings should be taken which are then averaged to give one single surface point. The longer the system is kept stationary, the more readings can be gathered to give a more accurate result and to average out the effect of machine vibration.
Extrapolate to zero method
Data is acquired whilst in contact and moving normal to the surface, either on the way in or whilst backing off. This is extrapolated to zero probe displacement position. It has the advantage that the measurement takes place at zero force, minimising the deflection on probe, stylus and CMM, and additionally is less sensitive to probe calibration.
There are two types of threshold method as described below. Type 1 takes data whilst driving the probe onto the part to a pre-set deflection threshold, whilst type 2 takes data whilst backing off to the pre-set deflection threshold.
A target deflection threshold should be set. The probe is driven onto the part until this target deflection threshold is seen, at which time the controller simultaneously stores all CMM axes together with the probe deflections - this is the data point.
A target deflection should be set. Additionally, an upper target deflection should be set which will enable a back off move to the target deflection to be executed at a constant velocity. The probe is driven onto the part until the upper target deflection is seen, at which time the motion should halt and a back off move should commence. When the target deflection is seen, the controller simultaneously stores all CMM axes together with the probe deflections - this is the data point.