Re: [CAD_CAM_EDM_DRO] Re: stepper vs servo

ddgman2001 wrote:

>I was speaking of positional error. I was under the assumption that
>the gecko system was closed-loop. Is this not the case? If not,
>what are the advantages of converting to servo?
>
>

OK, I tried to describe this in the following :

Since it is an open-loop system, the CNC

>computer has no idea how close the actual position is to the
>

commanded position, other than knowing it is within 128 encoder

counts, as exceeding that will cause the gecko servo to fault.

Within the 128 counts, a PID (Proportional, Integral, Derivative)

feedback control loop is implemented in hardware to give stable

and smooth following of the commanded position.

>
>

Now, let me clarify:

With the Gecko, the signals going between the computer and Gecko are
one-way:
From the computer to the Gecko drive. The only indication the computer
gets is
that a fault has or has not occured. If the drive faults, then the
computer had so
idea of actual position.

As long as the drive does not fault, then position control IS closed
loop between
the motor/encoder and the Gecko drive.

The only things you lose with a Gecko as opposed to a true servo are
continuous
following error monitoring, with the ability of having a sliding-scale
following
error limit that increases with velocity, and the ability to maintain
position
reading when in Estop. If you have a machine with manual handles, you
can use
EMC as a DRO when in Estop. You can also use EMC's logging and graphing
capability in the servo tuning process.

Jon


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