Re: [CAD_CAM_EDM_DRO] Re: Bridgport clone Retrofit

marc_e_davis wrote:

>Jon
>
>Thanks for the info. The motors are rated at 1430 RPM. I'm not sure
>if this is peek or what. I see your point about the cost of zero
>backlash couplings. I looked at those and wondered if anyone was
>using straight keyway sleeve couplings. Alignment seems problematic
>but still I wondered if it was done.
>
>The encoders are already mounted to the back of the servos. I do
>have some concerns here. There are 9 total wires coming from the
>servos. I'm guessing 2 for motor power, two for encoder power, and
>the rest for encoder signals. But it seems like a quad encoder would
>only need 2 wires. I know come servos have tachs or something called
>a resolver.
>
>

An encoder needs at least 4 wires - 2 for the A and B signals, as you
mention, and 2 more for
power. Most often a 3rd encoder channel is included, the "index" or Z
channel. This one
provides one pulse per revolution, and can be used to refine the
precision of the home switches.

9 wires could be :
2 for motor
2 for encoder power
3 for encoder signals
2 for tach? or a shield and safety ground?

Or :
2 for motor
6 for resolver
1 for shield

>Thanks for the info on the supply size. Do the Gecko drive regulate
>the voltage to the servos, or do they supply a PWM signal to the
>motors. I assumed that the Geckos just turned the motors on full
>blast until the encoder step count matched the step count requested
>by the control program.
>

Oh no, that would be the dreaded "bang-bang" controller, which would
never work for
a servo positioning system. If you tried this, you'd break belts or tip
the machine on its
side!

The PWM scheme is a form of regulation, the average voltage across the
motor is regulated
to provide a velocity as needed to minimize difference between commanded
and actual position.

> Does the Gecko provide some acceleration –
>deceleration? I figured this was the job of the control program.
>
>

It provides a very small amount of controlled acceleration. Mostly, the
CNC control program
needs to handle this.

Jon