Taking Points Perpendicular to Measuring Axis

[[Ja...]]

Hi all just a quick one

I am measuring some OD slot widths all around a diameter using different probe angle each time. How can I make sure that when taking point, my probe is perpendicular to the plane, and not on an angle (see attached). Just to avoid any cosign error etc....

Thank you!

Point Axis.JPG

[[Je...]]

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Hi Jack. Great question. If you don't want a super long answer, just read the last paragraph.

Cosine error is not a real risk in Calypso and with modern cmms as it is, for example, with a dial indicator. Instead, we talk about projection and projection error. We also make sure the stylus shaft is not making contact.

The cmm controller records raw coordinate data from the center point of the probe, not the contact point, which Calypso then assigns a stylus radius correction to. The probe does not need to vector perpendicular to the workpiece's normal, although it could be argued that this is still best practice. Active sensors are adept at knowing when to trigger a point, how to reduce deflection and how to measure various material rigidities. The Navigator technology on VAST sensors makes probe vectors occur more like a spaceship getting a gravity assist from a planet than like the familiar parachute landing of traditional probing.

Passive sensors such as an XXT are also capable, especially with shorter, lighter stylii, but do exhibit less projection error when vectoring normal.

There are multiple methods that Calypso uses to project points onto a workpiece to obtain actual values. I've attached a handy graphic from the Calypso manual that explains projection of the point feature (also found on pages 246-250 in the '23 manual). A few of the point feature types such as plane point will allow a normal workpiece vector to be obtained and constrained to before taking the actual measurement. Scanning adds other considerations such as scanning speed and point density (speeds and feeds). Curves add yet another layer of projection variables to consider, but it looks like your present question doesn't pertain to curves.


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[[Ja...]]

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[[SH...]]

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Under resources there is an option for space point mode, you can change it to plane point in your template program. I think it is possible to change it globally. I usually work with plane points.

Calypso___Space_point_modes.pdf

[[To...]]

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When using Define Points, typically they are Touch Points and they will snap to the closest primary axis. Create a secondary alignment, rotating so that a primary axis is parallel with the slot.

Go to CAD > Pre-assignment for new features. (Can also be found under Resources) Select the secondary alignment and leave this window open. You can close this window when you're done.

Touch the CAD model on both sides to create your Symmetry Point. Notice the secondary alignment is set on the feature. Click Ok to close your Symmetry Point.

Re-open feature and points should stay perpendicular to sides of slot.

The next step is something I do to align the 2 points directly opposite each other. Click Strategy, then double-click on either of the Probing Points to open up location details. Zero out the X and Y fields of both points and the points will be aligned with each other.

This can also be done when creating touch points with the probe.