CNC Repair Tip #3: Fanuc CNC Position Switch Parameters (or PSW’s)
Attention: Please read the Terms of Use for this site before proceeding.
Position switch parameters are used primarily to ensure that one or more axes are positioned within a specified distance of a target position. In my experience, they are typically used to ensure that the machine tool is correctly positioned for some auxiliary function such as automatic tool changes or pallet changes. In other words, you can set a plus and minus limit for a target position (such as the ideal ATC position) and the CNC will consider the movement complete if the machine position for the axis is at or between the plus and minus values. The CNC will send a signal to the PMC (ladder) to verify that the axis is in the correct position for a particular function to take place. Generally speaking, if you are not at or between the plus and minus values, you may be unable to perform certain functions safely and the CNC will not allow these functions to work. PSW’s are not used on all machines. Even if the machine has the ability to use them, they may not be written into the PMC ladder or there may be no values set in the NC parameters for this function.
For example, your machine may have the ability to operate an ATC main arm in a jog mode for ATC recovery or maintenance. However (for some unknown reason)the arm jog function is not working. If all the required conditions have been satisfied for the arm to move but it will not, you may be at an axis position that is outside of the plus and minus values set in the PSW parameters. This situation does not usually result in an error message on-screen and can be overlooked in troubleshooting.
From what I’ve seen,on most newer Fanuc controls (i.e. 16,18,21,30i,31i, etc) the PSW parameters start at 6901. NC parameter 6910-6919 are where the axes are assigned to the available PSW’s. Values are set according to axis number (such as “1″ for X, “2″ for Y, etc). Note that they do not have to be in order, necessarily. 6910 (“axis corresponding with the first PSW”) could be set to “2″ for use with the Y axis and 6911 (“axis corresponding with the second PSW”) could be set to a “1″ for use with the X axis. In most cases, you would not need to adjust any of these parameters differently from the factory settings.
The parameters you would usually deal with will be between NC parameter 6930-6959. 6930-6939 are maximum operation range settings (or positive direction limits) and 6950-6959 are minimum operation range settings (or negative direction limits).
Keep in mind that we are talking about direction and to watch the sign of the target position. If, for example, my ideal ATC position for the Y axis of a machine is -1.300mm (machine position) and I want to set a positive and negative limit in the PSW’s for this ideal position that is plus and minus 0.100mm. The setting for the maximum range would be -1.200mm. This would be .100mm in the positive (or less negative) direction from the target position. The setting for the minimum range would be-1.400, or 0.100mm in the negative direction from the target position.
On the Fanuc 15-M control, the plus and minus range settings start at NC parameter 5280.
When you can’t come up with any reason why something isn’t working or moving when the diagnostics seem to indicate that it should, you might check your machine positions versus the PSW settings.
Check out www.pinpointcnc.com for machine repair information, procedures and other products
Go to www.cncalarm.com for machine alarms and details
Go to www.toyookivalve.blogspot.com for information on Toyooki products
Go to Fanuc Control Central for all Fanuc related posts
Filed Under CNC Repair Tips, Fanuc Control | Leave a Comment
Tagged With cnc repair, cnc service, cnc services, fanuc, Fanuc Control, fanuc controls, machine repair, position switch parameters, psw