servos motor gecko DRO encoder?

[mike10]

with a servo motor setup can i turn off power to motors and have the encoders act like a digital readout? then turn motors back on when im ready for nc use?

[jed102]

Hi Mike,

I would really like to know if there are any servo drivers at this time that would have that feature also. It would be so good! I hope someone can help us here.

Frank

[fkaCarel]

If you split the A/B signals, in such a way that they feed the servo driver and the DRO you have what you want. This splitting is offcourse the principle. I expect to be virtually shot down here for the proposition. If you use a DRO that uses the same type of signals (A/B) the principle of lineals and encoders is the same. This excludes the DRO's for the Chinese LCD lineals, yes, sorry, they are the cheapest. The next (computing) problem is: you have to bring encoder resolution, pitch and realistic read out in line. So you need an adjustable (in this aspect) DRO.

[andy55]

if you wire the encoders to encoder counters in the pc and have a cnc controller that supports that (EMC), then you can power off the motors and have the encoders act like a DRO.
encoder counting hardware is around $200 (mesa, ppmc, vital etc., usually pci cards, see http://wiki.linuxcnc.org/cgi-bin/emc...orted_Hardware )

[jed102]

Nothing's simple eh! I'd pay a few hundred extra for a turnkey setup, but I wouldn't have the time for that much fiddling, though I'm sure some people might attempt such an endeavor. Thanks for the input!

Frank

[NC Cams]

Bridgeport did exactly as you suggest on their DX-32 based CNC systems that used a BMDC card. These were used on lathes, mills, and VMC's. This system was "state of the art" on 386, 486 and pentium 133's way back in 1995 thru early Y2K but fell by the wayside when Bridgeport went bust.

The motor encoders on the X & Y ran the DRO for the system both with and without power. For reasons that involved hysterisis problems, they ran the DRO off of the linear encoder when in manual mode on Z. They then switched over to the motor mounted encoders when the motors were "locked onto the quill" for 3D motorized milling.

The process involved some sophisticated encoder interfacing that I have not seen incorporated in anything but high end CNC retrofit systems.

Can it be done? Yes.

Has anybody done it even with the faster, more powerful computers that are even "free" in recycling centers today? Sadly, no outside of decidedly high end systems.

I content too much reliance on canned code in Windows and too expensive to do anymore via off loading the machine control to dedicated PLC's. Maybe you can't do with PCI that you could do with ISA slots. Those who know perhaps can explain why.

Maybe GREX will do someday what the defunct BMDC/DX-32 already did....

[jed102]

It seems like it's three steps forward and two steps backwards. It's amazing what they could do 10 years ago with old technology, and yes I really hope grex or someone will do something.

Frank

[fkaCarel]

Well, here a DRO connected to a processor via a serial-bus. The central processor reads the servo processors real position and sends this untranslated (hexadecimal), but converted from encoder resolution to 1/100mm to the DRO processor. There it is converted to decimal and displayed. Each unit has it's own adress, so multiple units can be used.

But this is to be used with an embedded computer, where all the functions are subdivided. There is a big chance that they never will be connected to a PC. You can see in post 4 what the costs are. The materials and possibilities are there, there only is no market.

[Mariss Freimanis]

I posted a circuit that opto-isolates (splits) the encoder outputs; one pair goes to the servodrive, the other pair goes to the PC for DRO use. This way all sorts and numbers of encoders can be powered by the PC +5VDC or other external supply.

There is at least one breakout board mfg that may run with it and incorporate that circuit.

Mariss

[jed102]

This is all very encouraging. I'll be keeping my eyes peeled, meanwhile I'm still waiting for the new Rutex servo driver with dro functions that is supposed to be in the works. I'm not holding my breath though!

Frank

[DennisCNC]

You can get this http://www.rogersmachine.net/encoderinterface.html and it will do what you want.

[jed102]

The problem with that board for me is that it won't work with the Mach3/G-rex combo and likely not with Deskcnc which I need to run my high count encoders.

Frank