Siemens SIMOVERT MASTERDRIVES Manual page 204

Functions
NOTE
RELMOD = 0
(U883=0)
NOTE
7-38
Relative positioning
In the case of relative positioning, also known as incremental travel,
movement takes place over a specified distance. This movement is
initiated by a positive edge on POS_ON (enable positioning) or transfer
with positive edge in transfer type SPV_RIE_TYP = 0.
Re-triggering of this movement is possible at any time. In this case, the
remaining distance is disregarded and a new relative distance is
traveled from the time of triggering.
Example: Actual value = 12567
Setpoint = 5000
New target position: 12567 + 5000 = 17567
Setting the homing on the fly changes the actual value. As a result, the
target position reached depends on the displacement of the measuring
system caused by homing on the fly. This can, however, be selected to
be dependent on the RELMOD mode (U883) (see next section).
The software limit switches refer to the sum of the distance (actual
value) and interrupt relative positioning when the software limit switch is
reached. Further movement can only take place in the direction
opposite to that in which the software limit switch was approached.
The relative movement is interrupted if the POS-ON is removed before
the target position is reached or a positive edge in given on SPV_RIE.
In this case, the remaining distance is deleted.
Recommendations:
if a relative movement is to be interrupted, i.e. without again travelling
the total relative distance, the speed setpoint on U851 can be set to 0%
by an analog switch. Stopping then takes place on the ramp. When
switched again to a valid setpoint, the axis travels to the old setpoint
position, i.e. the remaining distance will then be traveled.
Relative positioning mode
For relative positioning (POS_TYP_ACT = 1), the actual value from the
position value content of source U850.2 is used, as in all other modes.
This means that, when homing on the fly, the corrected setpoint is
taken into the travel distance calculation (SET = ACT).
The positioner behaves in accordance with correct control principles. In
the case of a rotary axis, the correction is carried out by the shortest
path. This may mean that a reversal of direction is possible, especially
if the correction value > 1/2 x axis cycle.
6SE7087-6QX70 (Version AG)
Compendium Motion Control
05.2006
Siemens AG
SIMOVERT MASTERDRIVES