
B-63943EN/02 9.STOP AND EMERGENCY STOP
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9.5 EMERGENCY STOP SIGNAL
CAUTION
Using the emergency stop signal effectively enables the design of safe machine
tools. See "Cautions for configuring an emergency stop circuit in compliance with
safety standards."
The emergency stop signal is provided to bring a machine tool to an emergency
stop. It is input to the CNC controller and αi (α) series power supply module.
The power supply module outputs a motor power MCC control signal, which can be
used to switch the power applied to the power supply module on and off. An
emergency stop signal is usually generated by closing the B contact of a
pushbutton switch.
When the emergency stop signal (*ESP) contact is closed, the CNC controller
enters the emergency stop released state, such that the servo and spindle motors
can be controlled and operated.
When the emergency stop signal (*ESP) contact opens, the CNC controller is reset
and enters the emergency stop state, and the servo and spindle motors stop.
Inputting an emergency stop signal causes the servo motor power to be shut off
through the IGBT, bringing the servo motor to a dynamic brake stop. Even in this
case, however, a servo motor attached to a vertical axis can move under the force
of gravity. To overcome this problem, use a servo motor with a brake. By using
relevant parameters, it is also possible to decelerate the servo motor to a stop, and
then to shut off the servo motor power.
While the spindle motor is running, shutting off the motor power to the spindle
amplifier allows the spindle motor to continue running under its own inertia, which
may be quite dangerous. With an αi (α) series amplifier, when the emergency
stop signal (*ESP) contact opens, it is possible to confirm that the spindle motor is
decelerated to a stop, and then to shut off the spindle motor power through the
IGBT.
When the motor power to both servo and spindle amplifiers is shut off through the
IGBT, the power supply module outputs a motor power MCC control signal, which
can be used to directly shut off the power with an external line contactor.
The CNC controller is designed to detect overtravel by using a software limit
function. Normally, no hardware limit switch is required to detect overtravel. If
the machine goes beyond a software limit because of a servo feedback failure,
however, it is necessary to provide a stroke end limit switch, which should be
connected so that the emergency stop signal can be used to stop the machine.
Fig. 9.5 shows an example showing how to make connections for the emergency
stop signal with this CNC controller and αi (α) series servo amplifier.