On Wed, 10 Apr 2019, dan...@austin.rr.com wrote:

Date: Wed, 10 Apr 2019 20:39:06 +0000
From: dan...@austin.rr.com
Reply-To: "Enhanced Machine Controller (EMC)"
To: "'Enhanced Machine Controller (EMC)'" <emc-users@lists.sourceforge.net>
Cc: "'Enhanced Machine Controller (EMC)'" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] Hardware emcmot?

From: "andy pugh"
To: "Enhanced Machine Controller (EMC)"
Sent: Wednesday April 10 2019 1:46:17PM
Subject: Re: [Emc-users] Hardware emcmot?

On Wed, 10 Apr 2019 at 19:43,  wrote:

> Actually I *don't* want to run a form of Linux. Since it's
> HW, the tasks can be hardcoded for bare metal

I wonder if the Mesa "SoftDMC" would do what you want?


        Hmm maybe so!

        Although it is key to modulate beam power at ~5KHz scaled with the
reciprocal of the instantaneous velocity and an accompanying motion
command param. Not the motion command target feedrate but the
instantaneous velocity after acceleration curves are applied. This
prevents burning more energy per inch than specified during accel

        The vector sum is easy to sum squares, but then you have reciprocal
of the square root to create. You know, it doesn't have to be perfect,
I wonder if a polynomial for reciprocal-of-square-root would suffice?
Much faster esp since multiplying 32 bit numbers could in theory
overflow a 32 bit reg (although the velocity to do that seems

        The same is true of any solution, except the bulk 98% of the base
requirement tasks are already there. No nontrapezoidal accel.

        There seems to be a lack of arc blending though, and I've seem the
result of poor trajectory planning on certain laser-cut files. Ones
that have like 1000 linear motion commands per inch (that number might
be hyperbole) and poor path smoothing, I think due to pixellation
causing irrelevant right-angle turns for only a few thousandth of an
inch. It ran *really* slow on something that was actually not a whole
lot of exceptionally high detail. Some of that could be path smoothing
approximated in the CAM stage.


Emc-users mailing list

I notice that you ordered a copy of SoftDMC from our webstore. I suspect This is not the best way to accomplish laser modulation with LinuxCNC

If you use our hardware, I think the best way would be to use our DataPainter
module for Hostmot2. Unfortunately this does not have a driver yet but could be accessed via raw register access in a real time hal component

This implements a FIFOed data stream (bitstream or PWM) that can be "position locked" to a motion axis or a multi-axis length vector for arbitrary path painting. In addition it has front-end (realtime) scaling of the PWM so that PWM duty cycle is the product of FIFO PWM data times real time (probably scaled/lincurved velocity) data.

The 1 KHz or so servo thread update rate is not a real limitation here since the data painting interpolates between motions (possibly scale) waypoints

Its addition it has start and stop position registers to allow gating the data stream at position breakpoints

This will support modulation rates to the hundreds of KHz

Misssing bits in LinuxCNC are some standard scheme to include position
synchronized data either embedded in the gcode or via external files

Peter Wallace
Mesa Electronics

Emc-users mailing list

Reply via email to