Siemens S7-300 - Page 101

Machine and cam data
9.14 Cam data
FM 352 electronic cam controller
Operating Instructions, 05/2011, A5E01071724-03
101
Lead time
Address
relative
Name Type Initial value Comment
+ 10.0 LTIME INT 0 Lead time
Range:
(0 to 53686) x 100 µs with max. 16 cams
(0 to 65535) x 100 µs with max. 32, 64 or
128 cams
You can compensate any delays caused by the connected switchgear by setting a lead time. Define
the lead time with a resolution of 100 µs. You can assign one lead time to each cam. The lead time
applies to the cam start and cam end.
Anticipation distance
The anticipation distance of a cam is calculated continuously based on the current velocity and lead
time. The entire cam is shifted in direction of the actual value by this distance. The assigned range is
the "static range", and the range calculated based on the lead time is the "dynamic range".
Anticipation distance = [lead time] x [current velocity]
FM 352 calculates the anticipation distances of all cams within
1
/
4
of the longest assigned lead time.
A very high lead time setting for a cam reduces the frequency of the dynamic adjustment calculation.
Actual lead time
To calculate the actual lead time:
Determine the cam cycle time: This is the time that the FM 352 requires to complete processing of all
cams. It depends on the number of cams available.
Calculate the actual lead time based on the following formula:
/HDGWLPH LQWHJHU
DFW
/HDGWLPH
G
&DPF\FOHWLPH
&DPF\FOHWLPH

The identifiers have the following meanings:
Lead time
act
is the lead time set by the FM 352
Lead time
d
is your default setting.
Integer ( ) means that the values after the decimal point are ignored in the calculation of the
parenthesis.
The maximum error of the lead time
act
is always < [cam cycle time] x 4.
Example:
The following values are defined:
Number of cams: maximum of 32 cams
Cam cycle time: 40.96 µs
Lead time
V
= 1000 µs
Result: The result is an actual lead time of 983 µs
It is not allowed to implement a lead time in combination with an absolute encoder (SSI) and inverted
count direction.