Siemens SINUMERIK 840C Installation Instructions Manual page 1005

12 Functional Descriptions
12.20.8 Configuration help for generator operation and emergency retraction
Drive-autonomous stopping and retraction
Drive-autonomous stopping and retraction initiated by the NC must be used if a response as a
function of the control (i.e. interpolation) is no longer possible, for example, if a very fast
response is necessary. In this case the drive system responds within one IPO cycle by
outputting a setpoint for the configured axes/spindles. Here too, a distinction is made between
stopping and retraction.
After drive-autonomous stopping and retraction, a Power On reset is necessary.
Note:
If the drive bus between the NC and the drive is interrupted (loss of sign of life) stopping and
retraction can only be performed as an autonomous function of the drive.
However, this does not normally occur in conjunction with a power failure.
Generator operation
Generator operation is for cases where the energy of the DC link is not sufficient for a reliable
retraction (for a time of at least 5 IPO cycles). This function makes use of the kinetic energy of
the spindle or axis and feeds it back into the DC link in an optimum fashion. The DC link
voltage is maintained within the limits parameterized in the drive machine data using a two-
step voltage controller (see Start-up Guide Section 12).
The axis/spindle parameterized as the generator measures the DC link voltage in "ms cycles".
The DC link can therefore be backed up within a maximum of 2 ms.
The energy stored in the drive
2
E = 1/2 * *
with
= total mass moment of inertia of the drive
= angular velocity at the time of switchover to regenerative operation
is fed back with a degree of efficiency of approx. 90%.
For generator operation, especially on large machines with high-power infeed/regenerative
feedback units (55, 80, 120 kW) it is advisable to use a separate drive with a flywheel that
must only put in the friction losses once it has reached maximum velocity.
Of course, any drive on the machine can be used for this function as long as it is not directly
involved in controlled stopping or retraction.
Axes that are involved in gear couplings must be maintained are not suitable.
Note:
A minimum speed limit of the generator can also be a source of emergency retraction
response. This is useful if short interruptions in the voltage must be backed up in regenerative
operation.
Other comments:
Suitably rated pulse resistance modules must be used to prevent the DC link from becoming
too great when braking begins (stopping and retraction either as a function of the control or as
an autonomous function of the drive) and the drive responding with pulse suppression causing
uncontrolled coasting.
12–230
© Siemens AG 1992 All Rights Reserved
09.95
6FC5197- AA50
SINUMERIK 840C (IA)