Danfoss MCO 305 Design Manual page 8

MCO 305 Design Guide
User Units
The units for the drive or the slave and the master, respectively, can be defined by the user in any way
desired so that the user can work with meaningful measurements.
Starting with MCO 5.00 the factors SYNCFACTM / SYNCFACTS, POSFACT_Z / POSFACT_N are no longer
limited to small values
Internally, it is act as follows: Whenever a value must be multiplied by the gear factor (i.e. master incre-
ments per ms), at first it is looked if a multiplication will result in an overflow. If so, a factor (64 bit) is used
which consists of
SYNCFACTS/SYNCFACTM to multiply the delta_master.
If no overflow occurs, first it is multiplied by SYNCFACTS and then divided by SYNCFACTM.
Concerning the error we are dealing with, this means:
Normal case
Multiplying by SYNCFACTS has no error, but dividing by SYNCFACTM means that the result may be wrong by
1/2³² . That means that (worst case) such an error occurs every ms, i.e. that after 1193 hours (49,71 days)
we made an error of 1 qc (Slave).
Big factors
In that case, the used factor (SYNCFACTS/SYNCFACTM) itself could be wrong by 1/2³² . This means that in
the worst case an error of delta_master * 1/2³² occurs every ms. Assume that we have an encoder with
1000 counts (4000 qc) per revolution. Assume further, that we drive with 2000 rpm, i.e. we have a velocity
of 133 qc/ms. This means we make an error of 133 * 1/2³² per ms. From this follows that in worst case
(maximum error every ms always in same direction) we could have an error of 1 qc after 9 hours.
This should not be relevant in most applications.
User Units [UU]
All path information in motion commands are made in user units and are converted to quad-counts
internally. These also have an effect on all commands for the positioning: e.g. APOS.
The user can also select meaningful units for the CAM control in order to describe the curve for the master
and the slave, for example 1/100 mm, or 1/10 degrees in applications where a revolution is being observed.
In the CAM control, the maximum run distance of the slave or the slave cycle length are indicated in User
Units UU (qc).
You can standardize the unit with a factor. This factor is a fraction which consists of a numerator and
denominator:
1 User Unit UU =
par. 32-12 User Unit Numerator POSFACT_Z
par. 32-11 User Unit Denominator POSFACT_N
Scaling determines how many quad-counts make up a user unit. For example, if it is 50375/1000, then one
UU corresponds to exactly 50.375 qc.
NB!:
When user units are transferred into qc, then they get truncated. When qc are transferred into
user units, then they get rounded.
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par. 32 - 12 User Unit Numerator
par. 32 - 11 User Unit Denomintor
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