[BillTodd]

I'm brewing up much the same but with a home made computer board reading scales and stepping motors.

The step timer interrupt compares "where I am" with "where I want to be" and steps accordingly.

The "where I am" can change at any moment should a report be received from any of the 3 scale interrupts. (I read them with hardware because any lag will only serve to confuse it).

At the end of an x,y,z stepping sequence it works out the error on all 3 axes. Should any be outside tolerance it doesn't update the "where I want to be" to a new position. This means I get remedial steps to put it back on course.

Questions are, wil it do more remedial steps than moving steps, and, how tight can I put the tolerance

I only have to mount the scales and I can find out

Interesting idea Although,the missed steps may not be able to be corrected until the cause has been removed.

i.e. if it drops steps because of excess speed v load, will there be time to correct them before the next motion without increasing the frequency of the pulses thus exacerbating the speed v load problem?

(Well worth trying though )

[Robin Hewitt]

The fast traverse is a completely separate interrupt handler, precise placement only happens at speeds where the motors can handle an instantaneous reversal.

There is more work to do. When it encounters back lash it will tend to trail by the tolerance and I will need extra remedial steps. OTOH I'm not going to try to fix anything until it has had a chance to tell me what needs fixing.

I'm writing the code and everything runs in SRAM. I can recompile and upload all new in a matter of seconds. I am in control

[Marzan]

Hi Robin. What a brilliant idea. When you get it right you will have solved one of the major issues with using steppers. i would be interested in the outcome.I had another thought that if i had the knowhow would be worth pursuing. What if you had a PIC counting pulses sent my Mach 3 and then the PIC moved the stepper motor using the encoder to go to the correct position? Its probably complicated, and you would get some lag,but i would gladly put up with lag for accuracy.

[BillTodd]

What if you had a PIC counting pulses sent my Mach 3 and then the PIC moved the stepper motor using the encoder to go to the correct position?

Hmmm , That wouldn't be too difficult.

I use a PIC (16F84 and an L6219) to drive the Z motor on my engraver, it'll happily keep up with the step inputs from the controller using interrupts. It even has has a couple of unused timer/counters that could be used to track an encoder. Might be worth a look

[I still wonder, if you're going to add all this complexity you might be better of using proper servo-motors]

[Marzan]

Hmmm , That wouldn't be too difficult.


[I still wonder, if you're going to add all this complexity you might be better of using proper servo-motors]

Yeah. you could be right, but steppers and encoders on ebay are a lot cheaper than servos, and if a cheap PIC could be made to act as a Pseudo closed loop it would be just as good for a lot less money for the DIYers

[aadityadengle]

tried the circuit with verniers too
but no data

[BillTodd]

tried the circuit with verniers too
but no data
:bs:

:bs: like that's going to get you an answer !

[komatias]

Hi Bill,

first off, you might want to think about adding a donate button to you signature!4 years later and there are people still interested in your work.

You got me to join another forum just to ask you a question. Pretty simple one it should be:

Do I need visual studio to get your program to install? I keep getting:

unable to register the dll ocx regsvr32 failed with exit code 0x4

on both my computers.

looking forward to your response.

Regards

George

[BillTodd]

Hi George,

The program is written in VB5, so you should not need VS at all.

It was designed for Windows 95. I have not tried it on Vista or Win7, so that may be the problem (can you install on a VM or as XP?).

the install script ireads:
Source: "d:\My Documents\VB5 projects\Logger\Vernier.exe"; DestDir: "{app}"; Flags: ignoreversion
Source: "e:\VB\System Files\MSVBVM50.dll"; DestDir: "{sys}"; Flags: onlyifdoesntexist uninsneveruninstall
Source: "e:\VB\System Files\OleAut32.dll"; DestDir: "{sys}"; Flags: onlyifdoesntexist sharedfile regserver
Source: "e:\VB\System Files\OlePro32.dll"; DestDir: "{sys}"; Flags: sharedfile regserver
Source: "e:\VB\System Files\AsycFilt.dll"; DestDir: "{sys}"; Flags: sharedfile
;Source: "e:\VB\System Files\Ctl3d32.dll"; DestDir: "{sys}"; Flags: sharedfile
Source: "e:\VB\System Files\StdOle2.tlb"; DestDir: "{sys}"; Flags: sharedfile
Source: "e:\VB\System Files\MSCOMM32.OCX"; DestDir: "{sys}"; Flags: sharedfile regserver
Source: "e:\VB\System Files\SCRRUN.DLL"; DestDir: "{sys}"; Flags: sharedfile
Source: "e:\VB\System Files\comcat v471\Comcat.dll"; DestDir: "{sys}"; Flags: sharedfile regserver

so there are only 4 files that require regserver.

4 years later and there are people still interested in your work.

4 years? I started this in 2005! that's the problem!

There are new scales out now that do not work with the PIC code (so be warned) At some point (way in the future), when I get one of the newer 21 bit devices I'll add it to the PIC.

Meanwhile, I get people like aadityadengle waving bs flags at me, because they cant get it working!

Is does work with the right scales:

[ame="http://www.youtube.com/watch?v=7R-qcTCTcxk"]PIC based DRO - YouTube[/ame]

[ayeff]

Reposted to correct forum - apologies.

Hi,

I was looking with great interest at Bill Todd's DRO designs, and I really want to build this one - I am quite at home with electronic assembly and PCB manufacture - but although an impressive amount of work has obviously gone into the design, the information downloaded appears to be fragmented and inconsistent, therefore I am having problems verifying schematic to PCB layout.

Having downloaded the Zip package for Version 1.2.05, I found the PCB layout PDF file, but there was no schematic. I downloaded the schematic separately from the forum, but one does not verify with the other. The PCB layout has numbered components and nets given, the schematic has no numbering - just question marks. I have tried tracing by eye, but there are several discrepancies. eg pin 7 of the DB9 goes nowhere on the schematic, but is connected on the PCB; there are 2 diode cathodes to 3.5V on the PCB, but only 1 on the schematic; there are 2 resistors to DB9 pin 4 on the PCB but only 1 shown on the schematic. I gave up at this point as clearly the schematic that I have is not the one that the PCB was netlisted and routed from.

Is there a schematic and PCB layout that are a matching set somewhere, or alternatively a definitive schematic somewhere that I can confidently use to netlist and route my own PCB from?

I really don't want to spoil a good project or waste time and money by going off half cock, so I trust some kind soul will be able to point me in the right direction.

Thanks.

[jhovel]

Why don't you send a PM (private message) to Bill?
I always believe in getting information directly form the "horses mouth".... He's friendly, helpful and doesn't bite

[BillTodd]

Hi All

Anyone wishing to build this project should bare in mind that I designed this some years ago for use with the 1.5V (positive frame) callipers that were around at the time. Modern callipers and scales have moved to a 3v (positive or floating frame) that require a different ground and power arrangement.

I've pretty much given up developing the PC application as there is a better Andriod tablet based app being developed by Yuriy
(Yuriy's Toys: Android DRO Project)

I will at some stage update the PIC code to work with Yuriy's DRO but I have little time these days (personal reasons) so it could be a while before i get a 'round tuit'

Regards

Bill Todd