Developments on my Home built 5C CNC Lathe - Polar interp. and Live tooling

for the X axis, do you have an encoder with index on the axis? If so you can home to that after the hall switch trips, for very good accuracy.

As for the C axis, you should be able to calibrate out the nonlinearity. I am not sure if a C axis can use a screw-comp file, but if not I am fairly sure that lincurve could be used to linearise the encoder.

The axes motors are stepper workalikes - they are brushless motors with an integrated closed loop servo-controller using an integrated 6200 pulse encoder which I believe does have an index segment but the encoder outputs are not available outside the motor - the control loop is closed internally. Motors are Clearpath SDSK series. In later versions of the motor firmware Clearpath provides a programmable output that can be set to show an equivalent of your concept ( they call it 'Precision homing), but my motor lags in version and appears not to be upgradeable. A new motor is around $350 - I think a better home sensor may be more economical in this case

Problem with linearising the C encoder is how to measure the actual angle during the process - I have good met. equipment for linear motion, not rotary.

EDIT - I am going with your idea - attached a single slot disc on the X motor shaft, with a slotted optical detector.

Seems this might not be so simple.
I have fitted the external index only disc and sensor and feed the sensor index detect signal to the 7I76 di14 input.
Since my servos are internal-closed loop, with no external encoder or index, connection are not defined in the HAL file to joint.n.index-enable from the encoder.n.index-enable for this ( or any) axis.

Can I just define these or is Linuxcnc now going to expect to close that stepper control loop itself, since an encoder is now sort of defined?

EDIT:
Not the way to do this - Cannot define another encoder anyway - the 7i76 has only one encoder input which is currently for the Caxis/Spindle. Probably going to do my own Homing Component to home X using the index edge as a simple discrete input.


Does anyone know if there is a Bit file for the MESA 7I76D to implement Stepgen Indexes? I have found various references to this being needed to use Homing with index without additional encoders available.
 

NoJo wrote:

Does anyone know if there is a Bit file for the MESA 7I76D to implement Stepgen Indexes? I have found various references to this being needed to use Homing with index without additional encoders available.

 

You need both to be using the correct firmware _and_ to be using the LinuxCNC development version to be able to use stepgen index. 

The 7i76D is a largely passive device, you would need to fine a 5i25(?) firmware with the stepgen index. 

Looking in the latest 5i25 firmware package the only pinout files that definitely contain a stepgen index are:
PIN_SVST8_4IM2SI_72
PIN_7I96_StepIDXD_51
And the latter only appears to offer an index on stepgen.0. 

It might be mechanically difficult to offer a stepgen index with a 7i76 as it does not offer very many input pins direct to the host FPGA. The GPIO on-board is serially-addressed and so isn't directly visible to the FPGA itself in the way that hardware pins are. 

I suggest asking Mesa.

Thanks Andy. Sorry, slipped up in my info there - I have the 7i92 with the 7i76 as the I/O part, so the bit file would be for the 7i92.
I think that route is becoming a little obtuse now...For kicks we made a few small changes/addition in source to implement the homing with index - moves to limit switch as normal, then moves till off limit and then look for index at low velocity.
that works so well, I might just compile and leave it like that. Dial gauge shows less that 1/3 of a 0.01mm division variation over a dozen home sequences. To progress with the rest, X homing stays like that for now!

PLEASE IGNORE THIS ISSUE. I see my mistake was to not install all the .deb files

I have built a Debian Package and installed it on my machine. I have however lost halcompile in the process - if I try run halcompile I get a message indicating the the command cannot be found.

The steps I went through to do the Debian Install are as follows:
sudo apt-get install dpkg-dev
cd linuxcnc-dev/debian
> ./configure uspace
> cd ..
dpkg-buildpackage -b -uc

At this stage, halcompile was still working
>sudo apt install ../linuxcnc-uspace-dev_2.9.0~pre0_amd64.deb 

Hereafter halcompile is no longer available.
I assume the .deb I have installed does not include halcompile? Please could you let me know how to adjust my process above such that the .deb does include halcompile