Messages

5351

General Mach Discussion / Re: Z Offset issue

« on: August 14, 2011, 09:26:30 PM »

As Hood stated you can enter it directly into the Zdro OR use the offset page which will do the same thing as you entering it .

(;-) TP

5352

General Mach Discussion / Re: Z Offset issue

« on: August 14, 2011, 02:17:18 PM »

The basic Z offset is the TOM (top of material  OR a standard reference point plus the value  of the guage). In yous examples when you touched off , +.002 for the shim and +.500 for the block. You would enter those values into the Zdro.

From the operators point of veiw it is not an offset but  a setting of the reference point of ORIGIN for Z  Z0.000. The machine uses a different set of coords to keep track of everthing important to position.

Did that help? or hurt (;-) TP

5353

General Mach Discussion / Re: Bit Height Offset

« on: August 14, 2011, 01:06:39 PM »

Here is the code that is in the button on the offsets page that does your function. It should be a good example to help get you started on macros.

Code "G92.2"
Call SetDRO(2, Abs(GetOEMDRO(1001)))

Hope that helps, (;-) TP

5354

General Mach Discussion / Re: Height Control for Router Table

« on: August 14, 2011, 12:56:11 PM »

We tried that with a Modio and the overall system responce (CB) was too slow at 10hzs.The reason I suggested the THC functions is that the LPT inputs sample at kernal speeds.

The second probem was getting the correction data to the Gcode buffer fast enough. You can run 1:1 on the buffer filling BUT now the machine was limited in overal performance and  speed because of waiting on the buffer.

To run a full buffer with a lot of look ahead (best for smoothness) you lost the ability to do the comp because the buffer loaded BEFORE the machine got to the point you needed to measue and apply the comp. ( catch 22).

The last option we tested was to take a linear encoder and use it to measure the height and use the quad output to drive the stepper drive directly that way it was geared to the surface measurements. With a modern digital servo drive running the Z this worked fairly well . BUT you had to swapaxis back and forth to have full control of Z and this made it VERY clunky to code and use. ALSO you woul dloose control of the positional state of Z each time and needed to refhome each time.

I still think the THC method could be made to work. WHen TOMc and Art developed the function Along with MUXing the ports it could be classed as a work of genius's in the DIY field of CNC.
BUT it would have to be fully investigated and tested. The nice part withte hTHC metod is you never loose postional control of the Z no matter how much the DTHC slapps it around(;-) MACH always knows where it SHOULD be.  SO Gcoding is never effected and it runs on the fly.

You mileage may vary based on local conditions, (;-) TP

5355

General Mach Discussion / Re: Height Control for Router Table

« on: August 14, 2011, 10:40:05 AM »

I guess the engineer that designed and built the unit did not know what he was talking about then. Shame to waste all that time on education. I'll let him know that he should not waste all his time working on such silly things that could never be possible.

But then again MAYBE that is why it works  so good.

You guys are funny,

(;-) TP

5356

General Mach Discussion / Re: Height Control for Router Table

« on: August 13, 2011, 10:46:31 PM »

(;-)No confusion here.

(;-)TP

5357

General Mach Discussion / Re: Height Control for Router Table

« on: August 13, 2011, 09:46:26 PM »

RRC , it is very easy to get the MACHINE to operate outside of the preset PID range. IF you use a feed screw that is too fast it is possible to outrun the pid because is not adjustable in most THCs and most pids are range specific to tuning SO if the PID is not use adjustable you MUST engineer the feedsytem to OPERATE in the boundaries of the set PID.

SAME goes true for the other end as well too slow or fine.

Get everything balanced and you have a very good working system.

Just a thought, (;-)

5358

General Mach Discussion / Re: Height Control for Router Table

« on: August 13, 2011, 09:30:44 PM »

You cannot look ahead any further than you can see data for, other than that you and the control are just guessing. If it gets faster than the the stiffness of the system you get the pogo so you slow the max velocity down to compensate.

The pid is used as PART of the sensoring of the arc voltages. IT tries to average out the input stream and make a smooth control output signal not just filter out high /low.

WITH the DTHC i am using now the first sign of unstable responce from the Z axis IS missed steps not motor oscillation. The system can run faster than the motor can phsically keep up. SO that tells me the pid is doing its job(;-).

HIYA CHris yes it is a complex subject. The DTHC is basicaly an advanced PLC system specifically engineered for the specific job of THC.  IF it was as easy as it looks everyone would be building one and they would be $10 a copy(;-).

COntour on the fly machining can be done BUT it takes alot of FAST control and responce to make it work well.  Probably well beyond MACH3 to do well

With  a buffered system you CAN run it 1:1 and fill as you go BUT the machining  MAY get choppy or slow as the drives may end up waiting on Data

Your milage may vary, (;-) TP

5359

General Mach Discussion / Re: header

« on: August 13, 2011, 06:53:42 PM »

Hey that looks like  one of my macros how did that get loose??

Restart your browser, it went away here after I restarted IE.

(;-) TP

5360

General Mach Discussion / Re: Height Control for Router Table

« on: August 13, 2011, 06:08:09 PM »

MIght want to check again on the pid on low cost DTHCs  THE thcup/down is only the fairly high speed digital INPUT to control the Z thru MACH.

 IF those signals are erratic then the Z will be erratic. The PID filtering takes place in the DTHC.

Being that Mach3 is NOT a real time controller your on the fly height correction calculations are not going to work well. Yes you can use #vars for Zheight control but ONCE the moves are loading into the buffer then that is it.  IF you try to calculate the variable at the point the #var is loaded into the buffer you will find you cannot comp something that has not happened yet. the next problem is the only way you have to update those vars are thru either the brains or the macropump. At a MAX of 10 updates per sec you will fall FAR short of the speed to do it well.

The ONLY access you have at that point IS the THC functions up/down to comp the surface heights based on what the DTHC sees. AND it is NOT value based it is like playing ping pong slapping  the ball back and forth. THe Z at that point will not even use the motor vel/accel parameters it just basically slaps the motor wide open in the direction it is to move and lets the DTHC deal with it being correct in height. Woops overshot slap it back in the other direction.  That is where the PID has to step in. Same basic princible as a servo motor drive.

Just a thought, (;-)TP