On Fri, 14 Mar 2008, Howard Chan wrote:
> Date: Fri, 14 Mar 2008 01:15:01 +0800
> From: Howard Chan <[EMAIL PROTECTED]>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] Can EMC2 support any 'AC Servo Motor'?
>
> Dear Peter,
>
> Would you explain detailed about why using the analog velocity input is
> better then pules/direction?
> Thank you!!
>
> Howard
Step and direction interfaces are usually used for simple systems
without a fully closed position loop (like step motor systems). While its
theoretically possible to use the encoder feedback with step and direction,
its not as direct as velocity or torque drive.
Another disadvantage of step & direction drives is that now you have
two feedback PID loops to tune, the amplifiers PID loop and EMCs PID loop. My
personal experience is that having the control locus in one place makes tuning
easier. Also with step and direction servo amplifiers its likely you would
need hardware step generation to reach the full speed capabilities of the
drives.
In addition you may need two separate operating systems to tune the
system, typically Windows to tune the amplifiers PID loop and Linux of course
for tuning EMCs PID loops.
One general advantage of using EMC for the total control loop (as you
would do using the amplifiers torque input and EMC for the PID loop), is that
now all of the motion control code is open and changeable. This may be
especially important as this is a university project. (no 'black boxes'!)
Peter Wallace
Mesa Electronics
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