Using the Virtual Probe Method

When calibrating a stylus tip in Calypso software it is recommended that you use Dynamic Tensor calibration at least in the initial calibration. This allows Calypso to gather the “bend data” of each individual stylus. Tensor or Geometric calibration may be used for recalibration purposes.

 

When using Dynamic Tensor calibration is not uncommon to receive this type of error.

This error requires you to rotate the reference sphere so that Calypso can access an unobstructed path around the reference sphere. To resolve this you may have reloaded the master probe and re-reference the sphere location. Then reloaded the stylus system and went through the entire calibration process.

 

Next time, try this procedure.

Creating a Set of Virtual Reference Spheres

Within the Stylus System Qualification dialog box click on the Reference Sphere Management icon.

This will open the Reference Sphere Management dialog. It is here that you will create the Virtual Reference Sphere positions. You may create as many positions as you would like. Below in Table 1 are listed the most used positions and these rotations might be a good start.

Above is your default Reference Sphere position screen. We will now add the Virtual Reference Sphere positions. To begin, click on the Copy as Virtual Reference Sphere button. This will bring up this next prompt.

Calypso will automatically select the next number for the reference sphere. Leave the number as is and click ok.

 

Now another reference sphere is added.

Change the Rotation Angle, in this case to 135 degrees, and Click Apply.

Let’s add another position. Click back on number 1 in the list and repeat the steps. Click on the Copy as Virtual Reference Sphere button. Name this one #3 and click ok. Highlight #3 in the list and change the rotation angle to 225.00 degrees and click Apply.

Repeat the steps until all of the positions are created.

Note: Inclination will be 135 on all examples

Ref Sphere Position           Rotation

1                                           45 

2                                          135

3                                          225

4                                          315

5                                          0

6                                          90

7                                          180

8                                          270

Remember all these steps where done to circumvent this error during calibration. Once you have completed the above steps it is not necessary to do them again. They will be stored for future use.

 

Using a Virtual Reference Sphere Position during calibration

The stylus will do a tensor calibration before this error appears.

Once this error has occurred change the Mode to Dyn. Tensor Re-qualification Mode.

Rotate the Master Sphere on the CMM table to the desired position that will allow for a dynamic calibration. It is important to just rotate around the existing position on the table. Do move it to some other location just rotate it around where it is currently located.

 

Open the Reference Sphere Management dialog

Now select the corresponding Virtual Reference Sphere that matches the new position on the table

Click Activate. This will now make, in this example, #3 active

You can now see that the Reference Sphere is Sphere #3

Now click on the Qualify Stylus button.

You are prompted to move the stylus and touch the stylus in the direction of the shaft.

 

This will now begin the dynamic tensor calibration. This is the scanning of the master ball since the tensor calibration portion was already completed prior to the error

The calibration is complete. Notice the Dynamic Qualification check mark is present and the Mode has changed back to Dynamic Tensor.

 

 

 

NOTE: By using the virtual sphere procedure, you first measure all styli in one position of the reference sphere and only then rotate the sphere to carry out the dynamic stylus qualification. Otherwise, you would have to re-qualify the sphere each time again.

CMM Calibration And These Tight Financial Times

By Mark Boucher, CMM Quarterly http://www.cmmquarterly.com/

With these pressing financial times may companies will be looking to cut costs. The Quality Control department will certainly be one of the areas that will be looked at. There have been some discussions about how often do we to have the coordinate measuring machine (CMM) calibrated. The standard for the industry has been yearly. Can this be pushed out to two years? Am I violating any customer specifications?

Yearly Calibrations

It has always been standard procedure to have the CMM calibrated yearly. This has been the accepted practice for good reason. One must look at how often your individual CMM is being used, the wear and tear, and the history of your CMM to properly determine if foregoing a calibration cycle is wise.

Before a decision is made about moving out the calibration cycle, it is highly recommended to check with your OEM to how this will affect the OEM warranty and how this will affect their standing behind the manufacturing specification of the CMM. Of course, this will be like checking with the oil company to see if the oil in a car really needs to be changed every 3,000 miles. Yearly calibration is a continuing revenue source for the OEMs but if you have already moved away from the OEM to a contracted 3rd party for calibrations then you have already addressed any concerns about the OEM warranty.

When looking at the CMM as a valued piece of your Quality department and your commitment to the customer to ensure you are producing a good product care must be given to your decision to push out the calibration. My personal recommendation is not to skip any calibration cycle unless the CMM is truly not being used on any regular basis. Even with some of the costs being demanded by the OEMs for calibration these days it is still important to have the preventative maintenance done yearly. Think about the cost associated with repairing a CMM that goes down during a production run. Trying to schedule a service repairman to get your CMM up and running in a timely manner can result in extra costs that may have been avoided if yearly maintenance had been done.

Important things to consider about the consequences of foregoing a yearly calibration:

How often do I use the CMM?
How will this affect my warranty?
How will this affect the OEMs standing behind the published accuracy specs?
Can I afford the cost and time associated with a ‘down’ machine?
Does my 3rd party calibration service offer preventative maintenance as part of their service?
Do I fully understand what my OEM offers when it comes to calibration?
How much money will I really be saving by pushing out the calibration cycle?
Will my customer be affected? Do they have any requirements that will prevent me from changing my calibration schedule?

3rd Party Calibration Services

When contracting a 3rd party calibration service it is important to establish trust in the contractor you choose. As with any contracting service I would recommend calling a few of their customers to get a good understanding how services that are offered where performed. Many of the contracted calibration services are former OEM service repairmen and are well qualified to perform calibrations and repair but it will be important to establish and understand exactly what services will be performed and what type of warranty comes with the service.

You can contact me at http://www.info@cmmquarterly.com/ if you would like a list of 3rd party calibration contractors.

This article is copyrighted. Please contact Mark Boucher at info@cmmquarterly.com for permission to reprint.