Danfoss VLT AutomationDrive FC 300 Series Selection Manual page 15

Positioning
In positioning mode, the drive controls
movement over a specific distance
(relative positioning) or to a specific
target (absolute positioning). The drive
calculates the motion profile based on
target position, speed reference and
ramp settings (see the examples in Fig. 1
and Fig. 2 on the right).
There are 3 positioning types using
different references for defining the
target position:
Absolute positioning
n
Target position is relative to the
defined zero point of the machine.
Relative positioning
n
Target position is relative to
the actual position of the machine.
Touch probe positioning
n
Target position is relative to a signal
on a digital input
This illustration (Fig. 3) shows the
different resulting target with a set
target position (reference) of 1000 and
starting position of 2000 for each of the
positioning types.
Synchronizing
In synchronizing mode, the drive fol-
lows the position of a master; multiple
drives can follow the same master. The
master signal can be an external signal,
for example, from an encoder, a virtual
master signal generated by a drive or
master positions transferred by fieldbus.
Gear ratio and position offset is adjust-
able by parameter.
Homing
With sensorless control and closed
loop control with an incremental
encoder, homing is required to create
a reference for the physical position of
Speed
Position
Fig. 1. Motion profile with linear ramps
Absolute
0
With absolute positioning, the drive moves backwards from the starting position
of 2000 to the absolute position of 1000 related to 0.
Relative
0
With relative positioning, the drive moves a distance of 1000 forward from
the starting position of 2000 ending at position 3000.
Touch probe
0
With touch probe positioning, the drive starts moving forward from the starting
position of 2000, detects the touch probe sensor and moves a distance of 1000
forward from the position of the touch probe sensor.
Fig. 3. IMC supports 3 positioning modes
the machine after power up. There are
several home functions with and with-
out sensor to choose from. The home
synchronizing function can be used to
continuously realign the home position
during operation when there is some
sort of slip in the system. For example
in case of sensorless control with an
induction motor or in case of slip in the
mechanical transmission.
Position
Fig. 2. Motion profile with S-ramps
1000 2000
1000 2000
1000 2000
Touch probe sensor
| Content | Danfoss Drives · DKDD.PB.302.A8.02
Speed
3000 4000
3000 4000
3000 4000
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