Re: [CAD_CAM_EDM_DRO] PC Control of Motion

Hi stan:

SOunds like what I'm trying, only without quite as much attention to timing.
I use the motherboard hi-res timer
and can pulse to about 1us per pulse with typical printer port i/o latency.
It could be done better in ASM, but
since I'm using the printer port, its about as fast as I can get it. My
primary table uses a dual 8255 and sends sin/cos info to my controllers. The
interrupts are good enough that mouse movement , etc. doesn't interfere
with movement. If you'd like to take a look, its at :
http://users.andara.com/~fenerty/master.htm

Art

----- Original Message -----
From: "Stan Krumme" <skrumme@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Thursday, August 31, 2000 9:45 PM
Subject: [CAD_CAM_EDM_DRO] PC Control of Motion


>
> Hello, my name is Stan and am a new member to this board. I have
> been reading the board off and on for past 6 months. I find myself
> working on the design of a motion control system based on a PC (for
> the fun of it), probbably PIII 450 Mhz or better. I read from this
> site and others, and seen the shareware code like CNC979. There
> seems quite a bit of discussion on controling stepper motors by
> sending step / dir pulses out a PC parallel port to control "black
> box" stepper motor controllers.
>
> My background is computer hardware/software design. The CNC seems
> like a lot of fun, and I am considering a retrofit to a Millrite
> vertical milling machine on 3 axis. Purpose of this post is to get
> any comments if others have implemented this or a similar approach,
> and any pros or cons.
>
> 1) Will run motion control in a DOS environment. Windows would not
> given enough contol in regards to timing, without much more expensive
> plug-in boards. In DOS I own the machine, so to speak. In windows,
> it tolerates me. I will run an RTC at, maybe 40 khz, providing 25 us
> per motion increment (loose numbers, but in the ballpark). Main
> program will compile in BAsic Pro 7 (considerable instrumentation
> programming experience). Interrupt drivers will be MASM assembly
> language.
>
> My have windows on system, using dual boot option for DOS. Real time
> clock interrupts from reprogramed RTC on PC motherboard or PIC RTC
> board.
>
> 2) Will use all PCI cards in this system, so that I/O will not
> SSSSLOW it down (at these interrupt rates), ISA is slow.
>
> 3) Stepper motors driven by 2 bipolar current amplifires, current
> set by 2 D/A ladder circuits (per motor). D/A ladder circuits driven
> by parallel input/output PCI interface board in PC. These boards are
> easy to find, up to 96 bits out and not too expensive (Computer
> Boards Inc or IoTech for instance) The program controls the bipolar
> current to the stepper windings. I could use a Analog output card,
> but its expensive and I do not need 12 or 16 bits resolution. 6 or 8
> bits should really be enough here. These motor winding currents are
> updated at 40 khz (or so). The steppers would be running more in a
> microstep mode. I would expect little problem from mechanical
> resonance.
>
> 3.5) CW and CCW Motion limits and home position switches run back to
> the PC thru the parallel interface. Panic STOP also. Panic stop
> also kills current to stepper motors (hardwired).
>
> 4) Should be able to easly maintain a VGA text screen with XYZ
> positions and velocities, current program step. Would have to see if
> graphic mode OK time wise.
>
> 5) Would avoid pesky IO devices when running these fast interrupt
> rates. Keyboard keys like cap_lock and scroll_lock lock interrupts
> out for 2ms (no no no!) The g code file to be loaded to EMS, XMS or
> ram disk. Command lines to be preparsed when first loaded. Will not
> run hard disk during motion control.
>
> 6) Program control during motion from small control panel run by
> micro, propably a PIC F877. Will communicate with PC via serial
> RS232 for such items as start/stop, xyz jogs, jog speed controls.
>
> PANIC BUTTON SHUR DOWN, a big heavy switch I can hit without breaking
> it (I can't imagine why)
>
> 7) The machine I am writing this on (slow PIII) peforms trig fuctions
> rather quickly, (floating point ops like SIN or COS in ~1 us). This
> puts me in the ball park to calculate and control machining ARCS on
> the fly! Calculated for each 25 us motion update. The straight
> lines are so much easier time wise.
>
> I like this approach.
>
> <A> It will be rigidly time locked by the RTC interrupts.
>
> <B> It will provide smooth motion from the stepper motors.
>
> <C> Ramp up /down & other fine points to be provided by
> properly written code
>
> <D> A Pentium III can do this, the horsepower is there.
>
> Has this approach been implemented by anyone? What has been
> their results?
>
>
> Thanks for reading this long winded post,
> Stan
>
>
>
>
>
>
>
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