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I built my own CNC router with the long axis (I called it X for various reasons) at about 2.7m. It's all on 8020 profile and no matter how I tweaked it, I could never get the gantry to move in a straight line. It would shift reliably +/- 0.1mm (or about 0.005in), so I had an accuracy problem that was too large for my liking.

 

I got this same plot over and over at multiple Y locations, so lincurve  would be a good solution here together with offset .

Essentially, lincurve lets you define an equation of sorts, then lets you map the x value to the y value. In this case, I would map the input of my X of where the spindle is to the output offset I want to move my Y axis. The reverse of the error you see in the graph above. Then I use that offset and implement it in the controller using HAL offset.

The "equation" that you give lincurve however is not your usual y=f(x), but multiple points (up to 16) on the x,y graph. The lincurve link above explains it better than I would.

Here is a snippet from my HAL:
And voila:
 

Hi Peter;

Thanks, I will look into that receiver chip.

Just for others who might find problems getting their MPG to work; I had to make some modifications to the HAL file. (I am using LinuxCNC 2.9.2)

1) I decided to use the jog-vel-mode 1 over incremental because I was use to a VMC I used at my job that would Jog that way: For each axis I did:

setp axis.x.jog-vel-mode 1
setp axis.y.jog-vel-mode 1
setp axis.z.jog-vel-mode 1

Mode 1 does not need increment but jogs each axis (selected by a switch on the Pendant Control) continuously at the speed of the turning of the encoder wheel.

2) Next I had to add this line for the motion module:

net motion-in-position halui.mode.teleop hm2_7i76e.0.7i76.0.0.input-07

3) For each Axis x,y &z I:

setp axis.x.jog-scale 3 #(to lower the speed I could have put 0.5 for example)
net axis-select-x => axis.x.jog-enable
net axis-selected-count => axis.x.jog-counts

Input 7, above, is an input pin on my MESA card that is netted to a switch on the Pendant control. I also had to comment out all the places in the HAL file that had to do with incremental control. The pedant control and the MPG work fine now.

Thanks Again,
ajc




ajc

There is no way to use the 7I76E MPG inputs differentially
but typically MPG inputs are pretty slow so if you had
a noise issue you could just add a bit of RC filtering.
(or add a differential receiver chip like a 26LS32)

Hi,

I have a Differential MPG on my Pendant control (It has A+, A-,B+,B- and 5V and GND)  and because of the distance to the 7i76e card and the noise,  I would like to use this 100 turn encoder in the differential mode.   With the 7i76e in mode 2 there are two MPG possible on terminal 16 &17 and terminals 18 & 19.  Is there a way to connect one MPG in the differential mode on these terminals?   If so, exactly where and how would I connect them?  Also, is there any special lines I would have to add to my HAL file or INI file?

Thanks,
ajc

 

forum.linuxcnc.org/27-driver-boards/3559...ethernet-mesa-boards

Yes, for single ended encoders, the - A,B,Z inputs are left unconnected.

Hi Peter,
My pncconfig screen looks exactly like what you have for P! which is on the 7i85 card and I have my XYZ encoders configured as you show. Since I have TTL encoders with the index signal: I set up all the jumpers in the correct position. What confused me was the numbering and use of the word MUXed. As you can see the terminal numbers are not given and encoder x axis is numbered 0 which I take to mean the first 8 terminals and the Y to be the next 8 terminals and z the next 8 terminals. Is that correct?

Also since I am only using 2 signal wires, a power and a ground. I would connect the A+ and B+ to their terminals and the index to its terminal. The power and ground are easy to figure out . I would, of course leave A- & B - terminals unconnected with no pull-up resistor ---- Is that correct? My encoders are sinking about 35 ma to ground MAX. Their rated for up to 30 volts but I am using the 5 volts provided by the 7i85.

Thanks Again for your help!
ajc

If you are talking about encoder type (single ended vs differential),
this is selected by jumpers on the 7I85 card.

The 7I85 encoders are on the P1 tab. Note
that in this configuration, encoders 0..3
are on the 7I85 and the spindle encoder
(4) is on the 7I76E

 

As far as the stepgens go, the only per-pin hardware
option is  whether the outputs are inverted or not.
Here are 4 axis of stepgens setup in a typical manner:

 
 

Probably needs flashing firmware for use with 7i85, and most probably it is included in the downloads on the www.mesanet.com website.
Still, that does not explain grayed out stepgens, so what language are you using?
Check if UTF-8 is used as locale as some locales will cause such issues.

PCW wrote:

The problem is that the 10.10.10.1 address is a default route
That's an error in setting up the 10.10.10.1 interface

I set up the nic based on tommylight's sticky on "Mesa ethernet setup for 7i92, 7i96, 7i76E and other ethernet Mesa boards".  The nic is set with an address of 10.10.10.11 and the gateway is set to 10.10.10.1.
Everything seems to be working great now.

Tommy,

Thanks for getting back to me so quickly. Concerning my MPG; it has 4 wires, A+, A-, B+ and B-. It is 100 PPR but the 7i76e terminals only take A+ and B+ and of course the 5 volts. On my oscilloscope I get a pulse from A+ and B+ by connecting to the probe grounds to negative.. A and B signals are 90 degrees out of phase. Maybe I should just leave the A- and B- unconnected?

In reference to your suggestion to run a PID tuning; can that be done without running PNCongfig? If so how?

Agian, thanks for your help.

ajc

A couple things:

I missed your post about encoders

Whether encoders are muxed or not has no real effect
on configuration file setup or hardware setup.

Almost all mesa encoders (other than MPG encoders)
can be jumpered to select TTL or differential inputs.
This is true of the 7I76E and 7I85. Typically MPG inputs
are single ended, this means if you have a differential
output MPG, you only use the two  A,B lines and ignore
/A and /B

Typically 7I76E firmware with 7I85 or 7I85X puts the
first 4 encoders on the 7I85 or 7I85S
so that the sensible encoder/stepgen 0,1,2 = X,Y,Z
mapping can be used.

Also note that stepgen systems with encoder
feedback are rather complex and uncommon.
In fact, if you are setting up such a system,
its better to get a pure open loop stepgen
system configured and working before you
change over to encoder feedback

With pncconf if you setup encoder feedback
the hal file will have the proper connections
(feedback comes from the encoder)
 If setup without encoder feedback, the local
stepgen position feedback is used.

This may be pncconf version dependent
but current (2.9.2) does the right thing.

Note that tuning will be quite different
with stepgen feedback or encoder feedback
and with encoder feedback you must get
the stepgen scale and encoder scale  and directions
correct.



 

Hello,

First let me say I am a newbie and want to learn as much as I can from the wiser ones in this group.  Further,  I appreciate any and all help as I have been at this for over a year, on and off, trying to get my system working.  I purchased a 7i76E and 7i85 board from MESA and feel that there documentation (although very thorough but hard to digest) is, in parts, over my head .  MESA's support seems to be  lacking and that may be because I am not a programmer or a wizard at computers.  At this point in time, I would have not made the purchase knowing all the stress and time spent spinning my wheels. 

I have asked a question, recently, about MUXed encoders and grayed out areas of the pncconfig program with no reply.  Again its probably my fault because I asked the wrong question. Now I ran into another problem (one after another) concerning the "closedloop stepper signals" section of the HAL file (which I do  not know how it got in the HAL file, since I do not have a closed loop steppper). In any event, seems the pncconfig program wants to net the x-pos-fb signal to stepgen.00.position-fb.  This causes an error because I want the x-pos-fb signal to be connected to the x-axis encoder. In my logic (which is probably flawed)  the program should know that the x-axis encoder info should reflect the steppers pulse count and at the same time, verifying the ball screw movement. Very confusing on how this program logically looks at real world data.

Any help in clarifying what is meant by MUXed (MUX x 4 or MUX x 16) encoder vs a TTL or differential encoder would be appreciated.  I have TTL encoders and hope they will work with the above MESA cards. Also, I have a pendant control that has a MPG on it with x1, x10, x100  switch on it and will need help adding it to the HAL files.  The encoder on the Pendant seems to be differential as it has A+, A-, B+, B- wires.
In regards to the problem with x-pos-fb; I just commented out the lines where they were netted to stepgen position feedback .  Please, comment on this being the correct strategy.


Thanks,
ajc


 

@PCW
You need to set DI1 to RUN and DI2 to FWD/REV to work with the 7I76E
I think this is P3.01 = 1

From this list what should I be selecting based on your comment?  

 

forum.linuxcnc.org/27-driver-boards/3559...ethernet-mesa-boards
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