How to setup spindle speed feedback from TACHO?

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01 Dec 2019 18:13 #151681 by idea
I'm looking for soe guidance to setup spindle speed control feedback using the TACHO signal from the brushless motor controller (motor is up to ~20,000rpm (micro mill). So i'm not looking for tapping ability, but want to correct for the low inertia of the motor/spindle when running loaded / unload.

I have the PWM signal working, with start / stop and speed control working correctly. I've tried using the encoder / counter to setup feedback but I dont think that is the correct methodology.

The first stage i'm looking for is to convert the TACHO [true/false] into rps/rpm that would then be of use. Any thoughts on how to do this?

The [spindle-vel-fb-rps] signal should then feed into the PID loop already present in the HAL?
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01 Dec 2019 19:37 #151685 by PCW
If the tachometer output is a frequency output proportional to spindle speed then
an encoder is the proper way measure this frequency and present it as a hal pin

Converting the encoder velocity signal to RPM/RPS is done by setting the encoder scale

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01 Dec 2019 20:30 #151690 by idea
I tried to connect the encoder but it ignored the tacho net for both the A and Z of the encoder and connecting the pin to those two threw an error.

Will encoder work without the index pin [Z] connected?

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01 Dec 2019 20:42 - 01 Dec 2019 20:42 #151693 by PCW
1. You can connect the A and Z pins of the software encoder to the same signal
perhaps you have a hal connection error of some kind

2. if the pulse width can get narrower than 1 ms, you need to use a hardware encoder instead of a software encoder

3. Index is only needed for threading or tapping (and tapping would not work with a 1 count per turn signal)
Index is not needed for simple counting
Last edit: 01 Dec 2019 20:42 by PCW.

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01 Dec 2019 21:44 #151704 by idea
The spindle motor outputs 20 pulses per rotation, so at full speed ~20000rpm that is 2.5us pulse width, so software is out of the question.

It does not look like i can specify a hardware encoder on any given pin / i'm limited to what is setup in the hardware? so that would be using an encoder that is nominally associated with one of the axis steppers?

It may be easier to setup an MCU to read the tacho signal, PWM signal and then control the motor to respond to the changing load.

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02 Dec 2019 00:09 #151714 by PCW
Many 7I93 configurations include one or more hardware encoders
Since LinuxCNC can read the velocity (and filter/display it locally)
and has a full floating point PID with FF2,FF1, FF0 I limits E limits
etc I would think it likely simpler to do this in LinuxCNC

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03 Dec 2019 13:10 #151851 by andypugh
Your HAL file contains
loadrt hm2_eth board_ip="192.168.1.121" config="num_encoders=0 num_pwmgens=2 num_stepgens=4"

Try "num_encoders=1" and see if some encoder pins appear.

Then you just need to work out which IO pins they are on.

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04 Dec 2019 03:34 #151941 by idea
Thanks for the patience (seems to be a common theme with many variations) - I'll attempt to document in workflow for others.

Ok so i've added a 5th encoder (at some point i will add axis encoders and these are already wired) and linked A to the tacho line i have connected on I/O 46. This was by following the guide here [ wiki.linuxcnc.org/cgi-bin/wiki.pl?Editing_MESA_Bitfiles ] by making up a new bit file to add and assign an additional encoder (only the A line connected to the outside world).

Then loaded/flashed to the MESA 7i93 board, in my case by using;
sudo mesaflash --device 7i93 --addr 192.168.1.121 --write 7i93_svst2_4d_5.bit

Then readout to test
david@linuxcnc:~$ mesaflash --device 7i93 --readhmid
Configuration Name: HOSTMOT2

General configuration information:

  BoardName : MESA7I93
  FPGA Size: 9 KGates
  FPGA Pins: 144
  Number of IO Ports: 2
  Width of one I/O port: 24
  Clock Low frequency: 100.0000 MHz
  Clock High frequency: 200.0000 MHz
  IDROM Type: 3
  Instance Stride 0: 4
  Instance Stride 1: 64
  Register Stride 0: 256
  Register Stride 1: 256

Modules in configuration:

  Module: WatchDog
  There are 1 of WatchDog in configuration
  Version: 0
  Registers: 3
  BaseAddress: 0C00
  ClockFrequency: 100.000 MHz
  Register Stride: 256 bytes
  Instance Stride: 4 bytes

  Module: IOPort
  There are 2 of IOPort in configuration
  Version: 0
  Registers: 5
  BaseAddress: 1000
  ClockFrequency: 100.000 MHz
  Register Stride: 256 bytes
  Instance Stride: 4 bytes

  Module: QCount
  There are 5 of QCount in configuration
  Version: 2
  Registers: 5
  BaseAddress: 3000
  ClockFrequency: 100.000 MHz
  Register Stride: 256 bytes
  Instance Stride: 4 bytes

  Module: PWM
  There are 2 of PWM in configuration
  Version: 0
  Registers: 5
  BaseAddress: 4100
  ClockFrequency: 200.000 MHz
  Register Stride: 256 bytes
  Instance Stride: 4 bytes

  Module: StepGen
  There are 4 of StepGen in configuration
  Version: 2
  Registers: 10
  BaseAddress: 2000
  ClockFrequency: 100.000 MHz
  Register Stride: 256 bytes
  Instance Stride: 4 bytes

  Module: LED
  There are 1 of LED in configuration
  Version: 0
  Registers: 1
  BaseAddress: 0200
  ClockFrequency: 100.000 MHz
  Register Stride: 256 bytes
  Instance Stride: 4 bytes

Configuration pin-out:

IO Connections for P2
Pin#  I/O   Pri. func    Sec. func       Chan      Pin func        Pin Dir

 1      0   IOPort       StepGen          0        Step/Table1     (Out)
 3      1   IOPort       StepGen          0        Dir/Table2      (Out)
 5      2   IOPort       StepGen          1        Step/Table1     (Out)
 7      3   IOPort       StepGen          1        Dir/Table2      (Out)
 9      4   IOPort       QCount           0        Quad-A          (In)
11      5   IOPort       QCount           2        Quad-A          (In)
13      6   IOPort       QCount           0        Quad-B          (In)
15      7   IOPort       QCount           2        Quad-B          (In)
17      8   IOPort       QCount           0        Quad-IDX        (In)
19      9   IOPort       QCount           2        Quad-IDX        (In)
21     10   IOPort       QCount           1        Quad-A          (In)
23     11   IOPort       QCount           3        Quad-A          (In)
25     12   IOPort       QCount           1        Quad-B          (In)
27     13   IOPort       QCount           3        Quad-B          (In)
29     14   IOPort       QCount           1        Quad-IDX        (In)
31     15   IOPort       QCount           3        Quad-IDX        (In)
33     16   IOPort       StepGen          2        Step/Table1     (Out)
35     17   IOPort       StepGen          2        Dir/Table2      (Out)
37     18   IOPort       StepGen          3        Step/Table1     (Out)
39     19   IOPort       StepGen          3        Dir/Table2      (Out)
41     20   IOPort       PWM              0        PWM             (Out)
43     21   IOPort       PWM              0        Dir             (Out)
45     22   IOPort       PWM              1        PWM             (Out)
47     23   IOPort       PWM              1        Dir             (Out)

IO Connections for P1
Pin#  I/O   Pri. func    Sec. func       Chan      Pin func        Pin Dir

 1     24   IOPort       None           
 3     25   IOPort       None           
 5     26   IOPort       None           
 7     27   IOPort       None           
 9     28   IOPort       None           
11     29   IOPort       None           
13     30   IOPort       None           
15     31   IOPort       None           
17     32   IOPort       None           
19     33   IOPort       None           
21     34   IOPort       None           
23     35   IOPort       None           
25     36   IOPort       None           
27     37   IOPort       None           
29     38   IOPort       None           
31     39   IOPort       None           
33     40   IOPort       None           
35     41   IOPort       None           
37     42   IOPort       None           
39     43   IOPort       None           
41     44   IOPort       None           
43     45   IOPort       None           
45     46   IOPort       QCount           4        Quad-A          (In)
47     47   IOPort       None

So the next step is to update the hal, i'm struggling got find a clear explanation of how the spindle encoder is read out. The information in [ www.linuxcnc.org/docs/html/examples/spindle.html ] seems to be for software encoder. Any good threads or suggestions?
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04 Dec 2019 03:44 #151944 by PCW
you can read the hostmot2 manual page for description of the encoder pins
or you can launch LinuxCNC and just list all the encoder pins/params with:

halcmd show all *.encoder*

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06 Dec 2019 02:58 #152129 by idea
Ok, so I managed to get the spindle feedback working, but the only way was connect the rps lines which i then need to increase the multiplier to FF0=60 to get it running

Is there a better way to set this up?
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