Renishaw SP25

[Big John]

Hello,
At the moment we have a couple of CMM's with Renishaw PH10M heads and either a TP20 or a TP200 module.
We are thinking about buying a new CMM. We are planning to scan some products.
Hexagon recommended their own rotating head type HP-L. This looks quite fancy, except that I have heard that for calibration it needs 25 hits for each angle being used. If that is so, then we will lose plenty of time calibrating instead of measuring. At the moment we calibrate using 5 hits on the calibration sphere. (Minimal I know, but it seems to work for us)
The difference is 5 times longer!!

I have 3 questions:

Is the 25 hits correct?

If we were to buy a Renishaw SP25 how many calibration hits are needed on the sphere? I asked Renishaw, they replied that it is up to the software.

Concerning the HP-L or the SP25

Is it not possible to calibrate the first position with 25 hits, then the other angles scan the sphere?

Regards
John

[NinjaBadger]

Yes 25 is correct.

The SP25 takes less hits, but then does a series of scans around and over the sphere, which takes much longer than the Hexagon offering.


Obviously what you loose in calibration you would typically make up more than in use, scanning diameters and surfaces rather than taking touch hits.

[neil.challinor]

If you are scanning then you do need to take 25 hits over at least 3 levels and perform a scnrdv calibration as well (scans once around the equator of the sphere). However, if you only want to take discreet hits and use it like a touch trigger probe then you only need 15 hits, again spread over 3 levels. NinjaBadger is correct about the SP25. It takes an initial 5 hits on the sphere an then (from memory) does at least 8 scans in multiple positons & directions around the sphere taking around 2.5 to 3 minutes per tip angle which is considerably slower than the LSPX1 (HP-S-X1) - even if it's taking 25 hits.

[neil.challinor]

Another thing to take into consideration when comparing the SP25 to an LSPX1-H is that the LSPX1-H can handle styli up to 240mm long and, for star probes, up to 100mm horizontal. To achieve the same range with an SP25, you would need SP25-1 (20mm - 50mm), SP25-2 (50mm - 105mm) & SP25-3 (120mm - 200mm) modules.

[Big John]

Hello Ninja Badger and Neil,

Thank you both for your reactions.
From your answers I would say that the HP_L was the better choice.

John

[Jim Poehler]

Another consideration with the SP-25M, which we use, is that depending on the release version of PC-DMIS you use, the later versions have a tick box option to use partial scan only. That being said, once an initial calibration for a new tip has been completed you can check that box and a calibration will be completed with only 5 touch hits on the sphere. The software stores and remembers the scan data and ties it to the touch hit data during calibration For us, once I upgraded from V4.2 to 2009, I was able to reduce our calibration time from 6.5 hours to 1.5 for our rack of probe tips. Hope this information helps.

[neil.challinor]

It is true, you can use the reduced calibration method that only takes 5 points but this only updates the calibration values for touch trigger probing. If you are performing any type of scanning operation within your programs you need to do the longer calibration or the scanning parameters will not get updated.