Re: Handwheels with EMC

Fred Proctor wrote:

> From: Fred Proctor <proctor@...>
>
> Handwheel folks,
>
> I've been reading the recent posts on implementing handwheel encoders
> for moving axes. I know of a couple of ways to implement a handwheel:
>
> 1. analogous to electronic gearing. With this method, the handwheel
> encoder is read at the same time all the axis encoders are read. The
> encoder input for the fourth axis of the Servo To Go card would serve
> nicely for the handwheel.

Yes, I think this is the best way to do it.

> 2. As an alternative way to jog an axis. With this method, the GUI
> itself reads the handwheel, and sends jog messages to the controller.
> There are problems with latency with this method, since the GUI needs to
> compose jog commands and send them to the controller. As you change the
> handwheel speed, new commands need to be sent down. Advantages with this
> method are that the INI file accel/decel values are honored; incremental
> handwheel motion is truly incremental jogging; and multiple distributed
> pendants or panels, each with its own handwheel, can be supported.

Well, using more than one handwheel (MPG) at a time sounds tricky.
But, maybe implementing a joystick in the GUI, but handwheels in the
motion control, would be the best way for each.

>
> The advantages to the second method may not be enough to offset the
> latency. Accel/decel with the first method are controlled directly by
> you, so it may simply be a question of not being unreasonably rough with
> the wheel. Using detents and proper scaling with the first method, its
> incremental jogging is indistinguishable from the second method. The
> biggest problem with electronic gearing is that you can't have multiple
> GUIs each with its own handwheel, unless you wire the handwheel encoders
> from the pendant to the motion card. Noise becomes a problem as the
> cable length to the pendant gets long.

As for noise, the STG card does support differential signals. I've never had
a problem that required it, though.

> I plan on implementing handwheels using the first method, electronic
> gearing. This technique can also be adapted to do rigid tapping, where
> the Z axis is slaved to the feedback from the spindle encoder.

Great, I am waiting to try the rigid tapping, too!

Thanks,

Jon