The SureServo2 system gives you two ways to quickly stop the motor.
You can use a single digital input to tell the drive to override its motor control and ramp
down the motor which would be appropriate for your home shop or other applications that don’t
need to adhere to stringent safety requirements. Think of it as a poor man’s quick and dirty
but non-compliant ESTOP button. Or you can use the SureServo2’s built-in
STO, or safe torque off function, which is for fully compliant safety systems.
The key thing to know about the SureServo2’s STO function is that it instantly removes
power from the motor which means the motor will be left to free spin down on its own.
There is a separate video covering the STO function, so we are just
going to cover the motor override function in this video which is ideal for a quick,
simple, and inexpensive way to quickly shut down the motor in a controlled fashion.
Let’s do an example. This is the exact same hardware we used in the quick start video,
so I am not going to go into any detail about that here. But it is important to recognize
that the STO jumper that comes with the drive is installed to bypass STO. That ensures STO
can’t get in the way of our override demo. I did add a heavy pully to give us more inertia.
The quick thing to remember is Digital Input 8 defaults to the override function and expects a
normally closed switch. If you want to assign it to a different digital input, then change
Digital Input 8 to something else and assign the motor override code to the new digital input.
I did a factory reset, switched to speed mode and power cycled the drive. I can’t emphasize
that enough. You really do need to power cycle the drive after a mode change. If you can’t get
things to work after mode change, it’s usually because you forgot to do that power cycle.
I’ll enable the servo and turn up the potentiometer to get the motor spinning.
If I hit the motor override button, sure enough we get the motor override alarm code
and the motor quickly stops. It stopped quickly because by default,
the drive’s built-in dynamic braking is enabled. There is a whole video dedicated to explaining
how dynamic braking works so we won’t go into that here. Just know that it's enabled by default when the
motor override button is pressed and that it’s a very efficient way to ramp the motor down quickly
without generating overvoltage faults. When you release the motor override,
the fault indication goes away, and the motor starts right back up.
Let’s go to Parameter 1.032 and change it to a 10 to tell the drive
to let the motor free spin to a stop. This time when we hit the motor override button
the motor takes a much longer time while it free spins down.
I’m using speed mode here, but this motor override will work for all drive modes.
The problem with this simple motor override is, what happens if the motor override switch gets a
welded contact and it won’t open? You can punch the button all day long, but your machine won’t
stop when you most need it to. Or what if the switch gets stuck open or it isn’t wired correctly.
There are all kinds of things that can go wrong that can prevent a simple motor override like
this from working and in many applications where the ESTOP has to work or bad things happen,
you can’t afford to take that risk. What do you do? You build a proper redundant
ESTOP safety circuit that constantly tests itself and lets you know when something isn’t right.
The good news is, the SureServo2 drive has the required circuitry built in so it’s super easy
to do. Check out this video to learn how to set that up using the built-in STO function.
Meanwhile, click here to learn more about the SureServo2 system
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