Siemens SINAMICS S120 Function Manual page 260

Extended Functions
Function module "basic positioner"
Note
Velocity override is effective while traversing to the cam.
By changing the encoder data set, status signal r2684.11 (reference point set) is
reset.
The cam switch must be able to supply both a rising as well as also a falling edge.
For a reference point approach with evaluation of the encoder zero mark, for
increasing position actual values the 0/1 edge is evaluated and for decreasing
position actual values, the 1/0 edge. It is not possible to invert the edge evaluation
for the encoder zero mark.
If the length measuring system has several zero marks that are repeated in cyclic
intervals (e.g. an incremental, rotary measuring system), it must be carefully
ensured that the cam is adjusted so that always the same zero mark is evaluated.
The following factors can influence the behavior of the control signal "reference
cam":
– switching accuracy and time delay of the reference cam switch
– position controller clock cycle of the drive
– interpolation clock cycle of the drive
– temperature characteristics of the mechanical machine system
Reference point approach, step 2: Synchronizing to the reference zero mark
(encoder zero mark or external zero mark)
Reference cam available (p2607 = 1):
In step 2, the drive accelerates to the velocity, specified in p2608 (zero mark ap-
proach velocity) in the direction opposite to that specified using binector input
p2604 (reference point approach start direction). The zero mark is expected at a
distance p2609 (max. distance to the zero mark). The search for the zero mark is
active (status bit r2684.0 = "1" (reference point approach active)), as soon as the
drive leaves the cam (p2612 = "0") and it is located within the tolerance bandwidth
for the evaluation (p2609 – p2610). If the zero mark position is known (encoder
evaluation), then actual drive position can be synchronized with the zero mark. The
drive starts is reference point approach (refer to step 3). The distance moved be-
tween the end of the cam and the zero mark is displayed in diagnostics parameter
r2680 (difference between the cam – zero mark).
Encoder zero mark available (p0495 = 0), no reference cam (p2607 = 0):
Synchronization to the reference zero mark starts immediately after the signal at
binector input p2595 is detected (start referencing). The drive accelerates to the
velocity, specified in parameter p2608 (zero mark approach velocity) in the direc-
tion specified by the signal of binector input p2604 (reference point approach start
direction).
The drive synchronizes to the first zero mark. The drive continues to travel with the
same velocity and travel is started to the reference point (refer to step 3).
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SINAMICS S120 Function Manual, 03/2006 Edition