Acu-Rite CNC 3500i Benutzerhandbuch

2 Machining Fundamentals

The machine axes are equipped with position encoders that register 
the positions of the machine table or tool. Linear axes are usually 
equipped with linear encoders, rotary tables and tilting axes with angle 
encoders.

When a machine axis moves, the corresponding position encoder 
generates an electrical signal. The CNC evaluates this signal and 
calculates the precise actual position of the machine axis.

If there is a power interruption, the calculated position will no longer 
correspond to the actual position of the machine slide. To recover this 
association, incremental position encoders are provided with 
reference marks. The scales of the position encoders contain one or 
more reference marks that transmit a signal to the CNC when they are 
crossed over. From that signal the CNC can re-establish the 
assignment of displayed positions to machine positions. For linear 
encoders with distance-coded reference marks the machine axes 
need to move by no more than 20 mm, for angle encoders by no more 
than 20°.

With absolute encoders, an absolute position value is transmitted to 
the control immediately upon switch-on. In this way the assignment 
of the actual position to the machine slide position is re-established 
directly after switch-on.