I second the point about not using a PC. Most of the CNC reliability issues I see are with backplane card edge connectors for DC servo drives and connectors subject to vibration/chafing of gold plating and oxidation of tin plating. A consumer grade PC motherboard is not meant for machine vibration. USB keyboard, PCI slot and SATA connectors seem to be a weak point as their insertion lifetimes are on the order of 50 or so. I would prefer a 1 or 2 PCB solution with tightly coupled interconnects (possibly soldered) board to board just to eliminate potential sources of connector failure.
My still functional 29 year old Bridgeport Interact 412 uses a Heidenhain 151 CNC controller. It's 12MHz TMS9995 microprocessor is surrounded with TTL counters for encoder position and associated logic that generates 0-10V spindle and brush DC servo command data. Any single core 1GHz A9 would run circles around what I have now. The cost of a PC versus a purpose-built embedded CNC controller is not an issue for me as long as the controller does not creep into the thousands of $$. Machine reliability and up time come first but safety is right up there as well. You can imagine what servo runaway is like when an encoder cable is broken. In my case mouse chewed. I've been following the BBB discussions and think the BBB would work for the networking & GUI and any RT servo timing should be handled by a FPGA. The BBB's 200MHz PRUs are OK for a simple 3D machine but my 6 head pick and place has X & Y axes, (12) Nema 11 stepper motors and 112 pneumatic feeders. A little beyond a BBB's I/O count. We developed a FPGA based stepper algorithm using the popular DRV8825 Reprap microstepping driver. The 8825 phase current is dynamically varied based on RPM and these tables are stored in the FPGA. Changing phase current vs. RPM allows us to tune around motor and carriage resonance points. We took a Nema 17 stepper and had it spinning at 3000RPM with 40-bit speed resolution. At full speed the 32x microstepping clock was 320kHz. Probably something a PRU could do in assembly language but is more flexible with VHDL. I'm considering the BBB and a Spartan-6 cape for ~$100 and the Zynq-based Snickerdoodle for $62-$157. The TS-4900 also looks appealing. Dennis On Wed, Mar 23, 2016 at 6:27 AM, Erik Friesen < e...@aercon.net> wrote: > > I don't want bang for my buck. What I want is a control board I can drop > into my haas, and doing it with x86 isn't very feasible. Dropping a > embeddedarm ts4900 on a custom baseboard would be real slick, and it seems > that it could surely compete with the 1990's era motorola running at 40mhz. ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785351&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
