Home, Marker or both?

On an application I'm currently working on, the company that set the device up used several servo motors, and set up the homing routines as Home to Switch and Marker.

Now, every time I've done a servo, I've set it to home to switch only, whcih seems simpler, and more reliable since changing the motor won't affect the servo home position with a different marker location.

Why would somebody want to use the marker? Is there some specific benefit I'm not aware of?

Thanks!

TM

More accuracy

If you home to a switch only, you know that the motor shaft is in the vicinity of the switch. You don't know exactly where the motor shaft is compared to the last time you homed. If you home first to the switch then home to the marker, you know that you found the vicinity of the switch and then ran to the marker, which will be exactly the same motor shaft position every time.

I agree it seems to be a bit much, in fact a lot of the time this minor difference wouldn't matter, but in a super-precise positioning job where tolerances and repeatability have to be in the .001's, thats what the marker is for.

switch only

I started my first motion project 7 years ago by homing to a switch then marker. This servo was run through a belt and the first time the belt jumped a cog or broke, the home position was off. Now all my applications only home to a switch. I locate the switch to sense the final moving part. That way, if any part of the motion gets changed it should not effect my home position. I was told once why you would usse a marker, but I do not remember now. Maybe if you are using the servo for a cam???

Homing to a switch is the simplest (and comparable accurate if you use a good encoder, be it rotary or linear) and no matter where you move the motor, it will home to the marker.