Functions And Examples; Positioning - Danfoss MCO 305 Design Manual

MCO 305 Design Guide

Functions and Examples

Positioning

Basically the term positioning in connection with drives means moving the shaft to a specific position. In
order to obtain accurate positioning it is necessary to use a closed loop system to control the actual
position, based on position feedback from an encoder.
A positioning procedure with a closed loop positioning controller requires the following: Set velocity,
acceleration, deceleration and a target position; a velocity profile is calculated based on the actual position
of the shaft as well as the before mentioned parameters; the shaft is moved according to the velocity profile
until the target position is reached.
Typical applications where accurate positioning is required:
− Palletizers, for example stacking boxes on a pallet.
− Index tables, for example filling material into trays on a rotating table.
− Conveyors, for example when cutting material to length.
− Hoists, for example a lift stopping at different levels.
MCO 305 offers three main positioning types
− Absolute
− Relative
− Touch Probe
Absolute Positioning
Absolute positioning always relates to the absolute zero point of the system, this also means that the abso-
lute zero point must be defined before an absolute positioning procedure can be conducted. When using
incremental encoders the zero point is defined by means of a Home function, where the drive approaches a
reference switch, stops and defines the actual position as zero. When using absolute encoders the zero
point is given by the encoder.
If the starting position is 0 and with an absolute positioning to 150.000 the target position is 150.000, the
drive will thus move a distance of 150.000. If on the other hand the starting position is 100.000 and with an
absolute positioning to 150.000 the target position is still 150.000 but the drive will only move a distance of
50.000 because it moves to position 150.000 related to the zero point.
®
MG.33.L5.02 – VLT is a registered Danfoss trademark
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