RE: [CAD_CAM_EDM_DRO] servo runaway prevention

Chris,

There was nothing to generate a follow error in this case. The particular
setup uses only the encoder pulses for position and no tachs. Even if the
machine was sitting still it is in reality dithering between the encoder
pulses. Stop feeding it a pulse when it goes to far one way and instead of
reversing and moving to the next pulse and then repeating the process it
will continue to move the motor and never generate a position error because
you are not commanding a move and no movement is being recorded all the
while the table is heading for the stops. Even worse is if the machine is
accelerating hard so the amp is putting out high current. In this case you
would likely get a follow error once the commanded position exceeds the
actual by enough, but if the axis had picked up enough momentum the added
push of the motor going at full tilt could create a crash very quickly on a
short axis.

Encoder cables falling off is a really bad thing. I have taken to using
cable ties to secure the connectors. Don't ask how I figured this out.

Tim
[Denver, CO]

> -----Original Message-----
>
> A poster recently commented that he experienced a servo runaway and
> some slight machine damage when the encoder cable fell off.
>
> It would seem to me that a proper following error setting should shut
> the machine down very quickly in such a case it is connected to an
> emergency stop circuit which kills power to the amps. Alternatively,
> a circuit could be added to the amps which would shut them down if no
> motion [in the correct direction] is detected by the time the output
> ramp up reaches a certain limit.
>
> Having fun with the stepper machine & thinking about the servos that
> will be on the next one,
>
> Chris
>
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