Fanuc OM Height of riversal Spike

[F.Sharifi]

Hi All !
I have Renishaw Ball Bar system QC10 and i have working with to check CNC machine tools , i need to know what parameter related to height of riversal spike compensation on Fanuc OM ... many thanks for your hints !

[Dan Fritz]

I'm presuming that you're referring to "backlash compensation", which adds a bit of an extra motion whenever the axis reverses direction.

The backlash compensation parameters for the 0M are #535 (X), #536 (Y), and #537 (Z). The increment is in "detect units", which is the smallest unit your machine can detect using the pulse coders. On a machine with metric ballscrews, this increment is usually .001mm, although it can be .0005mm on some machines. For inch ballscrews, the increment is usually .0001 inch.

Be careful to not set a compensation value that is too large. Sometimes, when you measure backlash with an indicator or a touch-probe, there are other factors such as ballscrew "wind-up", looseness in the table ways, thrust bearing play, etc. Not all of the positioning error you see with an indicator will be from ballscrew backlash. A large amount of backlash indicates a mechanical problem which can not be corrected properly by using backlash compensation.

Use a dial indicator with a large amount of travel, then make a short program that moves the table back & forth at least several millimeters at a medium feedrate with a G04 dwell between each move. The position where it stops should be the same regardless of which direction you are approaching the position. Just step-feeding or using the handle pulse geenerator to move the axis back & forth may not give you a proper indication of backlash. Also try to measure backlash in several positions along the ballscrew because the backlash is usually greater in the middle where the most wear occurs. Use an average of your measurements to get best results along the entire length of the screw.

[F.Sharifi]

Dear Dan fritz
Many Thanks for your explanation regarding Back lash compensation , thats correct and i always for some kind of machine doing as you said , ...but the relation of riversal spike little bit different , that means if machine try to make circle G02 or G03 in each qouadrant of movment (0 - 90 - 180 - 270 degree of movment ) depend of drive or motor one of the Axis going forwards or backwards just opposit of correct direction ... in QC10 System ( BallBar Checking system ) we can see this error seperate than Backlash , based on my experience of many test on various machine and control system , uncorrect of backlash value and Miss match error or Motors the basic cause of it , at last in Heidehain system or Siemens we have Parametre for compensate of Riversal spike ,...but i dont know about fanuc , i thinks that must be but Fanuc using different title for that ...again thanks for your attention .