Siemens SINUMERIK 840D Function Manual page 753

MD35350 $MA_SPIND_POSITIONING_DIR (Direction of rotation while positioning to
standstill)
Exception:
If ACN, ACP, IC is used for positioning, the programmed direction of travel is activated.
The spindle is synchronized at the next zero mark of the spindle position actual-value encoder
and switches to the position control mode.
Whether the zero mark is found in the traversed path (except for IC), is monitored:
MD34060 $MA_REFP_MAX_MARKER_DIST (maximum distance to the reference mark)
If the speed defined in machine data:
MD35300 $MA_SPIND_POSCTRL_VELO (Positioning speed)
is reached before the spindle is synchronized, the spindle will continue to rotate at the
positioning activation speed (it is not accelerated further).
Case 2: Spindle synchronized
SPOS, M19 or SPOSA will switch the spindle to position control mode.
The acceleration from the following machine data is active:
MD35210 $MA_GEAR_STEP_POSCTRL_ACCEL (acceleration in position control mode)
The direction of rotation is defined by the programmed motion (ACP, ACN, IC, DC) or via the
pending distance-to-go.
The speed entered in
MD35300 $MA_SPIND_POSCTRL_VELO (position control activation speed)
is not exceeded in the machine data.
The travel path to the end position is calculated.
The spindle travels to the programmed end point optimally in terms of time. This means that the
end point is approached at the highest possible speed (maximum MD35300
$MA_SPIND_POSCTRL_VELO). Depending on the appropriate secondary conditions, the
phases 1 - 2 - 3 - 4 or 1- 3a - 4a are executed.
Phase 2
Case 1: Spindle not synchronized
When the spindle is synchronized, position control is activated.
The spindle rotates at the maximum speed stored in machine data:
MD35300 $MA_SPIND_POSCTRL_VELO
until the braking start point calculation identifies the point at which the programmed spindle
position can be approached accurately with the defined acceleration.
Case 2: Spindle synchronized
To reach the end point, the spindle is accelerated up to the speed defined in machine data:
MD35300 $MA_SPIND_POSCTRL_VELO.
This is not exceeded.
The braking start point calculation identifies when the programmed spindle position can be
approached accurately at the acceleration defined in machine data:
Axes and spindles
Function Manual, 06/2019, A5E47437747B AA
S1: Spindles
18.2 Operating modes
753