Mesa 7i71 - Stepgen on Digital Output for ATC

Hey guys,

I´m currently continuing the retrofit of a Brother TC211 .
The machine is running with the following setup:

• Mesa 4i65
• Mesa 7i33TA for 4 Servo-Drives
• Mesa 7i44 for SSerial connected Boards
• Mesa 7i70 for 24V Inputs
• Mesa 7i71 for 24V Outputs
• Mesa 7i73 for Pendant

The toolchanger motor on the machine was changed to a stepper motor with reduction gear, as the old motor was not functioning anymore.
My first tests were done with an  external Step/dir generator  (with a Pot for the Speed)  that can be controlled with run/dir signals connected to the Mesa 7i71.
I also managed to read the toolchangers Encoder, which is BCD - feed into 4 Inputs on the Mesa 7i70 - with that I can count the 10 Tool Positions.

The control-loop for driving the Carousel to a specific tool pocket works more or less but only when the Stepper is driving the carousel at a low speed.
When the Speed is raised (with the Pot on the Step/dir generator) the Carousel overshoots the destined position.

So that was not an optimal solution, thats why thought about directly driving the stepper Motor from within linuxcnc. 
The problem now was how to generate the necessary step/dir signals. 

I experimented with a software stepgen, driving two Mesa 7i71 digital outputs as step and dir, which worked, but the velocity is very low.
Maybe someone has an idea why the stepgen output could be so low? Could it already be limited by the Mesa 7i71s switching output?

Im very open to other Ideas how to drive the Stepper motor with the setup I have.

Thanks in advance


 

The limit with the 7I71 is the servo thread period
(the maximum possible step rate would be 1/2 the servo thread rate)

If you have a free connector in the 4I65, step/dir outputs could be added there,
though they would likely need to be buffered. (or you have to be very careful
with wiring so you don't accidentally connect the bare FPGA pins to a voltage
outside the  0 to 5V range)

Thanks for the feedback Peter,

I bought a Mesa 7i52S, might be a bit overkill for just the tool changer but maybe I might add additional axes in the future, who knows..

As I understand, I need a firmware that adds the 7i52s ?

Thanks in advance

Yes, the 7I52S would need specific firmware.
What is the name of the current firmware you are using?

Its this one:
 
from this post:

PCW wrote:

 

Attachment not found

Should have version 43 SSerial

 
With a mesa 7i44 and a mesa 7i33TA connected to the 4i65 rn
It would also be interesting if its possible to use RS485 on the 7i52S to read data from the drives

I can add a 7I52S to that configuration but it would require that you
renumber the 7I33 encoders (due to the mixing  of muxed and non
muxed encoders). Is that OK?

 (the 7I33 encoders would end up as 0,2,4,6
instead of 0,1,2,3)
 

That should be no Problem.
I will have to rename them in the HAL file then, right ?
Also is there a way to use RS485 on the 7i52S ?

Thanks in advance

 

Had issues making it fit so:

P1 7I33 Normal encoders and numbering
P2 7I52 Just 2 stepgens
P3 7I44 just 4 sserial ports

Had forgotten how small XC2S200 chips are...
A wee bit more may fit if you need something desperately
 

Thanks for your efforts, I will try this firmware.

For future proofing, are there newer alternatives for PC104 formfactor than the 4i65 which are supported ? I Liked the pcie connection to the fpga so far, as it was super stable all time. Or should i consider a ethernet connected board like 7i80HD-25 or similar for the future ?

Hey Peter,
I tested the firmware you provided.
The 7i33 and the 7i44 + connected SSerial Devices work properly,
but I have Problems getting the Stepgens on the 7i52S to work.
Maybe im getting something wrong, but when entering a value to .postion-cmd, shouldnt the Stepper move?

The Stepper driver is connected to COMM0:

Pin3 TX0A to Step-
Pin4 /TX0A to Step+
Pin5 TX0B to Dir-
Pin6 /TX0B to Dir+

Also :

For future proofing, are there newer alternatives for PC104 formfactor than the 4i65 which are supported ? I Liked the pcie connection to the fpga so far, as it was super stable all time. Or should i consider a ethernet connected board like 7i80HD-25 or similar for the future ?