ESAB Aristo RoboFeed 30-4, Service Manual

Page: 15 / 34

DESCRIPTION OF OPERATION
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© ESAB AB 2014
Current monitoring
Resistor R114 generates a voltage signal proportional to the motor current. This voltage is
applied to potential divider R105/R106 and the output is compared with a reference voltage
at voltage comparator IC14:11. The reference voltage is provided by the microprocessor via
R104.
The current limit is between 15 and 18 A on starting. After one second, this is reduced to a
lower value. The current limit is related to the pulse peak current.
If the current exceeds the current limit, IC14:2 interrupts the gate pulse to Q4. The current
falls, and Q4 conducts on the next gate pulse, which is again interrupted if the current is still
too high. This sequence continues until the motor current has fallen below the current limit.
Speed monitoring
Wire feed speed is monitored by the microprocessor on the circuit board. Wire feed is
stopped if the feed speed deviates from the set speed by more than 1.5 m/min for more than
5.1 seconds. The U8 displays fault code 11.
Braking
Capacitor C67 is charged via diode D31 when the motor starts. Zener diodes D33 and D34
limit the voltage to 15 V.
When optocoupler IC11 is energised, its output transistor conducts and connects capacitor
C67 to the gate of transistor Q2, which conducts and short-circuits the motor supply via
dynamic braking resistors R71 and R79. The resistors limit the current to about 20 A.
Reversed feed
Activation of relay RE13 reverses the feed direction, see Section “13AP2:2 Input signals” ,
page 20.
13AP1:5 Pulse generator input
The pulse generator, 13G1, is fitted to drive motor 13M1. It generates 60 pulses per
revolution, which means that, at a wire feed speed of 25 m/min, the pulse frequency is 6552
Hz.