870 HEIDENHAIN Technical Manual iTNC 530 HSCI
6.8.7 Braking the drives for an emergency stop and a power failure
In an emergency stop and power failure the spindle must be braked as quickly
as possible. If the braking energy cannot be drawn off quickly enough, the DC-
link voltage increases sharply. Under circumstances, the inverter could switch
off and the spindle coast to a stop. A powerful braking of the spindle also leads
to a high strain on the mechanics of the machine. Preferably the spindle should
be braked in an emergency stop by limiting the braking power.
Normally, in case of an emergency stop, the axes are braked at the limit of
current. This can create problems:
With gantry axes a mechanical offset can occur between the master and
slave axes.
A gear between spindle and motor can be overloaded.
In such cases, the axes should preferably be braked in an emergency stop by
adding an additional braking ramp.
Problems with inverters without regenerative power supplies (with braking
resistors) during braking mostly arise if the inverter is switched off too early.
The strain on the mechanics during braking is reduced, but can also be
influenced with braking strategies.
Inverters with regenerative power supplies usually do not develop problems
if they are switched off. The main concern here is for the mechanics of the
machine. If the maximum regenerative power of the inverter is exceeded
when braking the drives (during an emergency stop, for example), the axes
and spindle(s) coast to a stop. In this case it is sensible to define separate
maximum braking powers for each drive in MP2390.x. This will ensure that
each drive is braked as quickly as possible.
Limiting the braking power is also effective when braking the spindle with
M05, if the brake ramp in M05 (MP3411 and MP3412) is steeper than the
brake ramp when limiting the braking power.
Both of the above braking strategies are possible for axes and spindles. If
both braking strategies are activated for an axis or spindle, they do not
exclude each other; this means that in case of an emergency stop,
whichever strategy responds first takes effect.
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