
B-64004EN/02 1.OVERVIEW
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1 OVERVIEW
Setup for machining, which includes attaching and detaching a
workpiece to be machined, and moving it to the machining start point
while viewing it, is performed with the protection door opened. The
dual check safety function provides a means for ensuring a high level
of safety with the protection door opened.
The simplest method of ensuring safety when the protection door is
open is to shut off power to the motor drive circuit by configuring a
safety circuit with a safety relay module. In this case, however, no
movements can be made on a move axis (rotation axis). Moreover,
since the power is shut off, some time is required before machining
can be restarted. This drawback can be corrected by adding a motor
speed detector to ensure safety. However, the addition of an external
detector may pose a response problem, and the use of many safety
relay modules results in a large and complicated power magnetic
cabinet circuit.
With the dual check safety function, two independent CPUs built into
the CNC monitor the speed and position of motors in dual mode. An
error in speed and position is detected at high speed, and power to the
motor is shut off via two independent paths. Processing and data
related to safety is cross-checked by two CPUs. To prevent failures
from being built up, a safety-related hardware and software test must
be conducted at certain intervals time.
The dual check safety system need not have an external detector added.
Instead, only a detector built into a servo motor or spindle motor is
used. This configuration can be implemented only when those
motors, detectors built into motors, and amplifiers that are specified
by FANUC are used. When an abnormality related to safety occurs,
the dual check safety function stops operation safely.
The dual check safety function ensures safety with the power turned
on, so that an operator can open the protection door to work without
turning off the power. A major feature of the dual check safety
function is that the required time is very short from the detection of an
abnormality until the power is shut off. A cost advantage of the dual
check safety function is that external detectors and safety relays can
be eliminated or simplified.
If a position or speed mismatch is detected by a cross-check using two
CPUs, the safety function of the Dual Check Safety works the power
to be shut off (MCC off) to the motor drive circuit.