Siemens SINUMERIK 840C - Manual (Page 918)

09.01 12 Functional Descriptions
12.18.11 GI monitors
The velocity warning threshold is input as a percentage value of the maximum velocity (NC
MD 280* or 403*-410*) in NC MD 1448*/494*.
1)
The interface signal VELOCITY/SPEED WARNING THRESHOLD REACHED is automatically
reset when the following drive velocity drops below 7/8 of the warning threshold (hysteresis
characteristic).
The same also applies to following drive acceleration.
The percentage value of the maximum acceleration (MD 276* or 478*-485*) is derived from the
same machine data (NC MD 1448*494*) as the velocity.
In some applications, it is impossible to prevent the following drive from exceeding the
acceleration value specified in MD 276* or 478*-485*. In order to avoid the output of an alarm
in these cases, it is possible to deactivate the acceleration monitor by means of NC machine
data 1848*/526* bit 3 "Suppression of acceleration limitation". The acceleration of the following
drive produced by the leading drive movements is then output directly without limitation or
alarm message.
12.18.11.1.1 Velocity/speed limitation of ELG following axes
(as from SW 6.4)
Functionality to date
By linking the following axis to the leading axes of the ELG grouping, the velocity/acceleration
of the following axis is the sum of the leading velocity/acceleration multiplied by the speed ratio
plus a possible following axis override. Dependent on the parameterization and programming of
the leading axes, the maximum permissible values of the following axis may be exceeded.
When machining the workpiece, the maximum values of the following axis should normally not
be exceeded. As the velocity/acceleration is limited when the maximum velocity is reached, the
position reference of the link would be lost. To make sure that the following axis does not
exceed the maximum velocity, the user has to take appropriate measures as for example a
prior test of the part program.
For reasons of user support, the so-called "warning threshold for n
max
and a
max
" (MD 1448*)
configurable via machine data has been provided for.
If the warning threshold is exceeded, the axis-specific interface signal "velocity/acceleration
threshold warning reached" is set. By means of the interface signal, the value of the channel-
specific and/or axis-specific override could be changed as a countermeasure via the PLC-
program such that the actual velocity/acceleration of the following axis is reduced below the
maximum values.
In view of the relatively long reaction time caused by the PLC cycle time, this method can be
used only under certain conditions to solve the above mentioned problem.
Description of the new functionality
In order to achieve a more dynamic behavior of the velocity/acceleration limitation of the
following axis, the leading axis velocity can now be adapted NCK-internally when the warning
threshold for n
max
and a
max
is reached using the new function "Velocity/acceleration limitation
of the following axis".
When this function is active, an acceleration stop is triggered for all enabled axes and spindles
of the mode group as soon as the warning threshold for n
max
or a
max
is exceeded.
Caution: The leading spindle is limited only to one value. A leading spindle is not taken into
account in the velocity limitation control. When starting a 2nd leading axis, this leading axis will
be limited or set to standstill.
1) As from SW 4: See functional description for ”Parameter set switchover”
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50 12–143
SINUMERIK 840C (IA)