8. EMERGENCY STOP SIGNAL
EMERGENCY STOP SIGNAL
We recommend appropriate use of the emergency stop signal when
designing a safe machine tool.
The emergency stop signal is for stopping the machine tool in an
emergency, and is input to the CNC controller, servo amplifier and spindle
amplifier. Generally, B–contact pushbutton switches are used for the
emergency stop signal.
When the emergency stop signal (*ESP) contact is closed, the CNC
controller is set to an emergency stop canceled state, and the servo
amplifier and spindle motor can be controlled and operated.
When the emergency stop signal (*ESP) contact is open, the CNC
controller is reset to an emergency stop state, and the servo amplifier and
spindle motor are decelerated and stopped.
In the case of the servo motor, the drive power supply of the servo
amplifier is turned OFF to activate a dynamic brake and stop servo motor
operation. Since gravity causes the servo motor used for the gravity shaft
to continue operation, you must consider using a servo motor with a
In the case of the spindle motor, if the drive power supply of the spindle
amplifier is suddenly turned OFF turning spindle operation, inertia causes
the spindle to continue operation, which is more dangerous. The spindle
motor must be controlled in such a way that deceleration and stopping of
spindle motor operation is confirmed before its drive power supply is
turned OFF when the emergency stop signal (*ESP) contact has become
The above have been taken into consideration in FANUC’s α series of
control amplifiers. On these control amplifiers, input the emergency stop
signal to the power supply module (PSM). Since the drive power supply
MCC control signal is output from the PSM, use this signal to control
ON/OFF switching of the drive power supply that is input to the power
Detection of overtravel by the software limit function is included in the
basic specifications of this CNC controller, and limit switches for regular
detection of overtravel are not required. However, if a malfunction in the
servo feedback system causes the machine tool to move beyond the
software limits, provide stroke end limit switches so that the emergency
stop signal functions to stop the machine tool.
Figure 8 shows a example of how the emergency stop signal is connected
when this CNC controller and an α series control amplifier are used.