
B–63502EN/01
30. SAFETY FUNCTIONS
NC FUNCTION
243
With the emergency stop, all commands stops, and the machine stops
immediately. Connect the “emergency stop” signal both to the control
unit and to the servo unit side.
When emergency stop is commanded, servo excitation is also reset, and
servo ready signal will also turn off. Move distance of the machine will
still be reflected in the actual position and machine position will not be
lost (Follow up function). After resetting the emergency stop, operation
can thus be continued without need of another reference point return.
To design a safe machine tool, use an emergency stop signal for it
properly.
The emergency stop signal is intended to bring a machine tool to an
emergency stop. It is input to the CNC control unit, servo amplifier, and
spindle amplifier. Generally, the B contact of a pushbutton switch is used
to input the emergency stop signal.
Closing the contact used for the emergency stop signal (*ESP) releases
the CNC unit from an emergency stop state, thus enabling it to control and
operate the servo motor and spindle motor.
Opening the contact used for the emergency stop signal (*ESP) resets the
CNC unit and brings it to an emergency stop. Opening the contact also
decelerates the servo motor and spindle motor to a stop.
Switching off the electric power of the servo amplifier for a servo motor
applies a dynamic brake to the servo motor. If the servo motor is used for
a horizontal axis, however, a load on the horizontal axis may drop to cause
the servo motor to rotate. To avoid this unintended motion, use a servo
motor with a brake or use another appropriate provision.
Switching off the electric power of the servo amplifier for a spindle motor
suddenly allows the spindle motor to keep rotating from force of habit,
which can be dangerous.
Avoiding this danger requires a control function that detects when the
emergency stop signal (*ESP) contact becomes open, and makes sure that
the spindle motor decelerates to a stop, then switches off the electric
power.
The FANUC control amplifier series is designed with considerations on
the behavior mentioned above. Just supply an emergency stop signal to
the power supply module (hereafter called PSM) of the control amplifier
series. The PSM outputs an electric power MCC control signal. This
signal can be used to switch on and off the electric power supplied to the
power supply module.
Basically, this CNC control unit is designed to use a software limit
function to detect overtravel, so an ordinary overtravel detection limit
switch is unnecessary. However, a stroke end limit switch must be
provided and connected to an emergency stop signal so that the
emergency stop signal can cause the machine to stop if the machine goes
over the software limit because of a servo feedback system failure.
The following diagram shows an example of connecting an emergency
stop signal when the CNC control unit and series control amplifier are
used.
30.1
EMERGENCY STOP