Siemens Simovert Masterdrives Compendium page 728

08.2012
Position resolution
P171
Actual value
weighting factor
P169/P170
P180.01 / 02
Siemens AG 6SE7087-6QX70 (Version AN)
SIMOVERT MASTERDRIVES
Parameter P171 defines the resolution of the encoder system used to
generate the overall position. The value should not be greater than the
practical maximum resolution of the encoder. It is important that the
complete traversing range be capable of representation in a 32-bit
double word. If this is not the case, the resolution must be reduced by
shift division.
The table below provides an overview of practical encoder resolutions:
Encoder system
Resolver
Encoder
Multiturn encoder
The resolution in P171 must be selected such that the positioning range
can be represented in a 32-bit double word.
The default of 4096 increments/revolution is adequate for most
positioning tasks.
The actual value weighting factor (AVWF) is used to transpose the
encoder increments into a physical unit. The unit can be defined freely,
and is referred to as the LU (Length Unit). LU is the length unit in which
the user prefers to specify his target positions. The weighting factor
specifies the traversing distance in the "number of length units LU"
corresponding to one position increment (after shift division) − including
all gear ratios, roll feed diameter, etc.
The preferred reference for the length unit LU in association with
positioning tasks is µm for linear axes and 0.001 degrees for rotary
axes.
Recommended Position Normalization for Positioning Axes
Recommended for linear axis:
1 LU = 1 µm
Recommended for rotary axis:
1 LU = 0.001°
The actual value weighting factor (AVWF) can be input by 2 different
methods:
a) Directly as a decimal number with 3 integer places and 8 decimal
places
b) As a fraction with a 20 bit numerator and a 20 bit denominator
Variant (b) will need to be used if the AVWF cannot be represented by
8 decimal places and where cumulative errors have to be avoided. This
applies in the case of rotary axes. The actual value weighting factor
(AVWF) must therefore be specified as a fraction for rotary axes if it
cannot be represented by 8 decimal places.
Compendium Motion Control
Practical max. resolution [increments/revolution]
2 12 = 4096
2 24 = 16777216
2 20 = 1048576
AVWF = traversing distance in µm
per increment [LU/inc]
AVWF = traversing distance in
1/1000ths of one degree
per increment [LU/inc]
Technology Option F01
9-37