RE: P.I.D.

["Pete Cook" <pete.cook-at-alltracorp.com>]

As listed here then machine is going to be springy around the desired
position - you have to get some error (out of position) and the CNC
generates some voltage to counteract the error and corrects some portion of
the error. For every encoder count there is some error voltage to
counteract.

The D gain is generally listed as the correction for the last error - if you
are out of postion by x encoder counts this adds in another x volts. If set
to high the machine will go into oscilation

I gain compensates for the cumulative error over many moves. If set to high
the machine can get mushy.

D Gain will take the springy feeling out of the machine.

An example - a servo with a drum and cable with a weight hanging on the
cable. At standstill the P Gain will cause the servo to come to some stable
point at some distance out of position (motor torque counterbalances the
load) Change the load and the system will stablize at a different point.

The D Gain will add some more compensation to bring the servo back into the
correct position no matter what the load.

These numbers will vary depending on the encoder counts (more or less counts
per inch) and servo response.

Pete

>
> P = 50
> The proportional gain for the axis servo. This value
> multiplies the error
> between commanded and actual position in user units, resulting in a
> contribution to the computed voltage for the motor amplifier.
> The units on
> the P gain are volts per user unit.
> I = 0
> The integral gain for the axis servo. The value multiplies
> the cumulative
> error between commanded and actual position in user units,
> resulting in a
> contribution to the computed voltage for the motor amplifier.
> The units on
> the I gain are volts per user unit-seconds.
> D = 0
> The derivative gain for the axis servo. The value multiplies
> the difference
> between the current and previous errors, resulting in a
> contribution to the
> computed voltage for the motor amplifier. The units on the D
> gain are volts
> per user unit per second.
>
>
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