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Page 25 of 53 POS-123-P-PFN 31.03.2021
5.4.2 VMODE (Methode of positioning)
Command Parameters Unit Group
VMODE x x= SDD|NC
CONTROL
The fundamental control structure can be changed with this parameter.
SDD: S troke- D ependent D eceleration. In this mode, stroke-dependent deceleration is activated. This
mode is the default mode and is suitable for most applications. With stroke-dependent deceleration
the drive comes to a controlled stop at the target position. From the deceleration setpoint the drive
then switches to closed loop control mode and moves accurately to the desired position. This
control structure is very robust and reacts insensitively to external influences such as fluctuating
pressures. One disadvantage is that the speed varies with the fluctuating pressure as the system
runs under open-loop control.
NC: N umerically C ontrolled. In this mode a position profile is generated internally. The system always
works under control and uses the following error to follow the position profile. The magnitude of the
following error is determined by the dynamics and the closed loop gain. The advantage is that the
speed is constant (regardless of external influences) due to the profile demand. Because of
continuous control, it is necessary not to run at 100 % speed, as otherwise the errors cannot be
corrected. 70… 80 % of the maximum speed is typical although especially the system behavior and
the load pressure should be taken into account when specifying the speed.
5.4.3 ACCEL (Acceleration)
Command Parameters Unit Group
ACCEL x x= 1… 20000 mm/s²
CONTROL (NC)
Specification of the setpoint acceleration in NC mode. The maximum acceleration must - in order to ensure
stable and vibration-free behaviour - be set smaller than the technically possible acceleration. Experience
shows that a factor of 3... 5 should be taken into account.
5.4.4 VMAX (Maximum speed in NC mode)
Command Parameters Unit Group
VMAX x x= 1… 2000 mm/s
CONTROL (NC)
Specification of the maximum speed in NC mode. This value is defined by the drive system and should be
specified as exactly as possible (not too high under any circumstances). The speed is scaled by means of the
external speed demand. The command is only active if the VMODE has been parameterized to NC. If the
speed of the drive differs between retraction and extension, the lower speed must be set.