Danfoss MCO 305 Design Manual page 31

MCO 305 Design Guide
Marker Synchronization (SYNCM)
Marker synchronization (SYNCM) is extended position synchronizing where an additional position correction
is done to align a slave marker with a master marker. Master and slave marker signals can be the encoder
zero pulse or external sensors connected to digital inputs. As with position synchronizing it is possible to
adjust gear-ratio and offset, in addition a marker ratio can be set e.g. 1 master marker to 3 slave markers
which mean that every master marker will be aligned with every 3
The marker signals can be monitored by defining a position window, only one marker (the first one) will be
accepted within the marker window and any marker signal outside the marker window will be ignored.
Without marker windows every marker signal including noise pulses and jitter will be accepted and used to
correct the slave position. The first master marker and first slave marker after starting are not monitored as
the system does not know where the first marker is supposed to be. After detecting the first marker the
anticipated position of the following markers is known as the marker distance must be specified by para-
meter individually for master and slave.
When starting marker synchronization the initial behavior will be like position synchronization but when the
first set of markers has been detected marker correction will start. Which markers to use for the first
marker correction can be defined by parameter 33-23, by defining the start behavior it is possible to define
whether the slave must always wait for the master, catch up with the master or make the smallest
correction, see parameter 33-23 for a detailed description of the available options. Homing procedures are
thus not necessary prior to starting as the marker correcting will automatically align the slave with the
master.
The slave must be faster and more dynamic than the master in order to make marker correction and main-
tain accurate synchronization both at maximum master velocity and during acceleration/deceleration. I.e.
the slave must be able to exceed the maximum velocity, acceleration and deceleration of the master to
allow it to make marker correction and to catch up if getting behind the master. Already during the design
phase it is thus important to consider making the least dynamic shaft the master as this shaft will anyway
be the limiting factor for the system performance.
Typical applications are:
Basically the same application types as position
synchronizing but where one or more of the
following is true:
− Automatic alignment after start is required.
− Gear-ratio cannot be set 100% correct.
− There is slip somewhere between the
encoder and the part the must be
synchronized.
− Varying distance between products.
Application Example: Packaging with Varying Product Distance and Slip
This application consists of two conveyors, 1 carrying empty boxes and another one carrying teddy bears,
the purpose of the machine is to put teddies into the boxes. Both boxes and teddies are moved by friction
and can thus move on the conveyor belt. It means that there is no fixed relationship between the encoders
and the position of box and teddy bear and the distance can vary. It is therefore necessary to use external
marker detection on both boxes (master) and teddies (slave) in order to synchronize the teddy bear
position to the box position. Alignment can be obtained by adjusting the physical position of the marker
detectors or by adjusting the position offset in parameter 33-12.
__ Functions and Examples __
Control behavior with marker synchronization
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MG.33.L5.02 – VLT is a registered Danfoss trademark
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slave marker.
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