Dear All,

I am using Sinamics S120 CU320-2 PN. In this servo unit LU is used. LU means how much mm or μm? 

Please someone explain me about this LU concept.

With LU you define your own unit. For rotary axes you maybe want to work with degrees, for linear axes you probably want to work with µm, mm, inches,....

So you decide and for that the parameter p2506 (LU per load revolution) is most important to set up! Important is always to consider the load side movement, not the motor movement!

1st example rotary axis:

Your load is a rotary movement doing 360 degree and you want to have a fine resolution of millidegree, so you set up p2506 = 360000 LU per load revolution. So then in your case 1 degree = 1000LU or 1LU = 1 milli degree. If you want to possition 90 degree you have to give a setpoint of 90000LU.

2nd example linear axis:

Your load is doing a linear movement controlled by a leadscrew (rotary motor + leadscrew). So you need to know the leadscrew pitch, lets say this is 10mm forward movement for one revolution. And you want to have a fine resolution in µm. So you set in p2506 = 10000 LU per load revolution. So 1mm = 1000LU or 1LU = 1µm in your case. If you want to position 50mm you have to give a setpoint of 50000LU.

Do the same thinking for speed (1000LU/min) and acceleration (1000LU/s²) -> for "LU" just put in your own unit that you think of , e.g. 1millidegree or 1µm from the examples above.