Back Check Circuit - Nachi RMU20-20 Instruction Manual

2.3.4 Back check circuit

Signal name
Robot power supply back
check 1+
Robot power supply back
check 1-
General safety output 1
back check 1+
back check 1-
General safety output 2
back check 2+
back check 2-
General safety output 3
back check 3+
back check 3-
Back check circuit with over current protection and input diagnosis
A back check circuit is provided in the RMU in order to monitor the magnet switch contacts which are tripped
by the safety outputs. In the back check circuit, a safety contact ("b" contact) driven by the safety output and an
auxiliary contact ("b" contact) of the magnet switch are connected in series so that if the main contact ("a"
contact) of the relay melts down making it impossible to release the contact, the other safety output can still be
turned off to shut off drive power surely and stop the robot safely.
*) If the back check input is not inputted, a back check fault will be detected when the output is ON.
Table 2-15 Back check
Circuit
Description
code
BK1+ Signal from magnet switch "b" contact.
BK1- Signal for detecting the welding (back
check) of the magnet switch
When being used as a slave unit, this is
regarded as a weld stuck detection signal
for "Slave failure" output signal (back
check).
BK2+ Signal from external safety relay and
BK2- magnet switch "b" contact
Signal for detecting the welding (back
check) of the magnet switch
BK3+ Signal from external safety relay and
BK3- magnet switch "b" contact
Signal for detecting the welding (back
check) of the magnet switch
BK4+ Signal from external safety relay and
BK4- magnet switch "b" contact
Signal for detecting the welding (back
check) of the magnet switch
2.3 Connected signals
Electrical specifications
Photo-coupler input
Rating DC26V
Input current 5mA
Over current protection provided
Photo-coupler input
Rating DC26V
Input current 5mA
Over current protection provided
Photo-coupler input
Rating DC26V
Input current 5mA
Over current protection provided
Photo-coupler input
Rating DC26V
Input current 5mA
Over current protection provided
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