Atlas Copco PowerMACS 4000, User Manual

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Tightening
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6.8 Servo and spindle protections
To avoid servo and spindle breakdowns there are a number of protections implemented in the servo
software. These protections aim to protect the servo and spindle from overheating and over current
failures.
6.8.1 Stall protection
The stall protection prot
ects the servo and the spindle if the spindle for some reason gets stuck and don‟t
have enough power to continue the rotation. The speed of the motor is constantly monitored and if it is too
low the servo shuts down the motor to protect from excessive heating due to high currents.
The speed limit is 274 rpm, measured on the motor. The spindle speed this corresponds to depends on
the gear ratio of the spindle, for some examples see the table below. If the motor run slower than this the
stall protection is activated.
Depending on the current level the protection works in different ways:
Below 20 A => No protection is active
Between 20 A and 42 A => It is allowed to stall for a maximum time of 5 s
Above 42 A => It is only allowed to stall 3 ms.
If the stall protection is activated the event “TC %d, Servo Driver Stalled“ is reported. In the cycle data the
error code “SERVO“ will be set.
6.8.2 How to avoid the problems
It is normally best for the spindle and the servo to run with medium speeds. With low speeds the
tightenings will take a long time and thus a lot of heat will have time to build up. With very low speeds the
stall protection will also be activated and cause problems.
Spindle type Stall speed limit
[rpm]
QST42-20CT 37
QST42-50CT 13
QST50-90CT 15
QST50-150CT 9
QST62-350CT 10
QST80-450CT 12