Passive vs active scanning stylus qualification.

[[Ow...]]

I don’t mess with our Duramax’s much, so this may be a redundant question but, ignorance is bliss Right?

On a Duramax CMM using the XXT-TL3 passive probe, you can qualify a horizontal star probe using the “Qualify Passive Stylus” mode on the reference sphere using, for example, position 2 (T135,R135) and the probe will scan the ball with all 4 probes and it will avoid the shaft section when needed.

However, when calibrating the same type of stylus system with an active scanning head (vast gold) using “Dynamic Tensor qualification”, it WILL NOT scan the sphere unless the whole equator of the sphere is accessible.
So, it will not avoid the shaft like it does automatically with “qualify passive” on a passive scanning head. In this position, two of the probes must be qualified with “tensor” only because it can’t access the full equator of the probe on all sides.

Why can a passive do this and an active not do it?

[[Ri...]]

The Qualify Passive Stylus routine allows up to 20% of the scanning routine to be exempted in order to avoid the Reference Sphere shaft. Dynamic Tensor does not but, there are routines that can be run which can dodge the Ref Sphere shaft and still retain the high speed stylus shaft bend characteristics, and all the other factors that scanning at 80mm/sec are present. With a XXT, passive scanning, the first time qualifying a stylus only gives you one choice, Qualify Passive Stylus. This routine takes quite a long time and if you stylus diameter is greater then 1.5 millimeters will not fall under that 20% threshold. With a star probe, all with 3mm diameter styli, I will be able to qualify 3 of my 5 styli with the Ref Sphere orientated in one of the 135 Tilt positions. To get the other two qualified, I will need to change stylus systems to the MasterProbe, rotate the Ref Sphere position 180 degrees, then run the Ref Sphere position routine. Now I can change back to the original Star Probe and qualify the remaining two positions. That's a lot of fooling around to qualify a Star Probe. The remedy is Geometry Requalification. Every time I qualify the Star Probe after getting all 5 styli qualified initially, I will run the Geometry Requalification mode. This is a 6 point qualification routine that takes much less time and I can get all 5 styli qualified with the Ref Sphere in a single orientation. This routine refreshes the size and location of the styli and leaves the bend characteristics of each styli shaft intact. The VAST Navigator stylus qualification routines have a similar method and choices. The very first time you need to qualify a styli to be used in a high speed part program, it must be done with Dynamic Tensor. This will require you give the styli 180 degrees of coverage. Again, this will likely require you to reposition the Ref Sphere or have another Ref Sphere on the table. Every qualification after the first, you will be able to use the Tensor-Requalification mode. It will look just like a Tensor mode but it will leave all the bend characteristics that Dynamic Tensor wrote to the probe file intact. If you qualify with Dynamic Tensor the first time and use Tensor after, you clear out all that information.

I edited this post to correct an error.

[[Ow...]]

Thank you, again, for your valuable input Richard.
We're qualifying a 3mm dia star probe with qualify passive on a 25mm sphere and yes it does take a long time but, scans the sphere with all 5 probes.
I guess I just find it somewhat unpleasant that DynamicTensor can't exempt 20% and still retain enough pressure and bending parameters to qualify.

[[Ri...]]

It's hard to say why Dynamic Tensor has 180 degrees of sphere coverage as a absolute requirement but that pain only needs to endured once. In theory anyway. After getting the initial Dynamic Tensor Qualification done, you can use the Tensor Requalification mode as your day in day out qualification tool. Some customers choose to re-run the Dynamic Tensor mode at some point i.e. once a month or once a week. It would require some testing to determine if that is necessary for your shop.

I edited this post to correct an error.

[[Ma...]]

Try using the Virtual Reference Procedure. I've attached a .pdf on how to use it.

Mark

[[Ow...]]

Thank you for adding the work-around instruction Mr Boucher.

[[Ja...]]

FWIW - Not doing a full dynamic tensor is too uncomfortable for me. I’ve seen how metal stress relieves itself over time, which has to affect rigidity to a certain extent. I would have to think the styli with metal shanks are subject to doing the same thing. As for non-metallic shanks, there are a few articles that pop up with a Google search that deal with how humidity affects carbon fiber. Granted the changes that we’re talking about in both these types are going to be very small, but when you’re trying to hold tolerances of a tenth (0.0001”) or two, that might be enough to make a difference.

[[Ow...]]

I've got a little mp4 video showing what the little Duramax can do automatically that the big vast-gold cannot do with the same size stylus's and sphere....but, apparently you can't load videos here.
All said though, I realize there is a minuscule difference between scanning passive and scanning dynamic tensor.

[[Ri...]]

With a 6 point qualification, you get stylus diameter and location. With Tensor, you get diameter, location, and bend characteristics. Two points measured on the sphere at the same location and along the same vector with one point at a low force and one point at a high force. The software looks at the differences of all the pairs of points and can develop a compensation to include with Stylus radius. With the XXT, there is Passive Qualification which has scan paths instead of point pairs. Dynamic Tensor has both. Dynamic Tensor is also writing more information to the probe file then just diameter, location and bend characteristics. Mass and rigidity and inertia are also in that file. The intent for this is for high speed scanning. When you're throwing that stylus system around at 60, 70, or 80 mm/sec and you want the same precision that you got with 10, 15, or 20 mm/sec, the software needs that additional information. The XXT does not and is not intended to scan at Navigator speeds so I can understand why it can dodge the probe shaft and the VAST Gold can't.

[[Ow...]]

Very true Richard.
I was feeling a little facetious comparing the two but, I do appreciate you elaborating on the differences. No Duramax is going to scan 80mm/sec for sure. 🤣

[[Ri...]]

no problem Owen. If you have any more questions, shoot me an email or give me a call. I'd be happy to help.

[[Ja...]]

Richard, you said "With Tensor, you get diameter, location, and bend characteristics." So is it safe to assume Dynamic Tensor is added for the Navigator high speed scanning?

[[To...]]

Jack, it's always my impression the Dynamic Tensor was to compensate for the inertia of the machine movement at higher speeds. Hence scanning at 5mm per second and then again at 50mm per second.

[[Ri...]]

Jack, yes, Dynamic Tensor is the qualification routine you must run if you are going to run at Navigator speeds. It writes more information to the probe file then the normal Tensor routine. You do not need to run the Dynamic Tensor routine each time you do a qualification though. Tensor Re-qualification runs a routine that looks like Tensor, but it leaves the additional information the initial qualification recorded to the probe file intact. If you run the Tensor routine after a Dynamic Tensor, you will wipe out that information. If you are running at Navigator speeds Thermo Fit extensions are recommended. Less mass and more rigidity.

I edited this post to correct an error

[[Aa...]]

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That's backwards. Dyn. Tensor Re-qualification only runs the scans at two different speeds (after taking a few probing points to ensure the reference sphere is correctly located to the ball), and overwrites the additional information. Dyn. Tensor Re-qualification can be run on a virtual reference sphere (where the location of the reference sphere doesn't matter.)
Tensor Re-qualification runs a routine that looks like Tensor, and leaves the additional information intact.

The difference between Tensor and Tensor Re-qualification is that Tensor will zero out the additional information.
The difference between Dyn. Tensor and Dyn. Tensor Re-qualification is that Dyn. Tensor will include the Tensor portion, and overwrite the tensor data.

[[Ri...]]

Aaron is absolutely correct. I apologize for the error. I was working from information a few versions old and without a Prismo 10/12/10 to play with.

[[Ja...]]

Got it. Thanks guys. I've been programming RDS/XXTs for so long I've forgotten most of the XT stuff - learning all over again.

[[Da...]]

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