4 bit parallel ADC for spindle gear control

I doubt anyone has tried this. And I am not sure it is a sensible thing to try. Why not use 4 output bits from HAL and use HAL logic to pick the required gear? That would also make it easy to not turn on the motor until the gear is selected.

johnmc wrote:

The problem is how can I convert a spindle speed S into a 4 bit logic that will allow the correct gear ratio to be activated.
I thought the 0 to 10 volt spindle speed would be divided by the analogue to digital converter with a 4 bit signal , and with the truth table select the correct speed gear ratio clutches .

I don't think that there is much point taking the digital speed signal in HAL out to the real world as an analogue signal, then converting it back to digital for further processing.

Does the lathe have a VFD or does it run a fixed speed in each gear?

I have a vaguely similar situation with my CNC lathe, albeit I have a VFD and only two speed ranges selected by electromagnetic clutch.

(I was going to post documentation links, but it looks like the main LinuxCNC.org web site is down at the moment)
One way to do what you want, though not a very elegant one, would be to use the HAL "lincurve" component. You could set up Lincurve to output a number based on spindle speed command. The number would be a binary representation of the combination of clutches required.
The reason that this is inelegant is that the output of Linucurve is floating-point, and converting to an integer format to extract the separate clutch signals might fall foul of rounding errors. Also it is not aware of spindle state, and will try to change gear any time the spindle speed command changes.

A better solution is probably a custom HAL component like the one I have for my lathe. Exactly what this would look like depends on how you want to control the spindle, whether gear-change with the spindle under load is allowed, whether gear change with the spindle spinning is allowed, etc.

The component will look like this (written in English rather than C)

make a set of params for the spindle speed ranges
make a set of params to define the clutch positions for each speed
;;
If the spindle is stopped, don't do anything
If the spindle speed command is less than threshold 1
Set the clutches for the lowest speed
Go into a waiting-for-stop state
If the spindle speed command is less than the second threshold
Set the clutches for the lowest speed
Go into a waiting-for-stop state
...
(Spindle Running, waiting for stop)
If the spindle speed < safe-to-change-gear speed
Go back to the top

The implementation on my lathe has a manual over-ride switch for situations where the spindle speed is set by the GUI. I only needed a 3-position switch for this (high, low, auto), your situation might be more interesting.

There are docs on the main LinuxCNC site on both writing custom HAL components and on Classic Ladder, the built-in PLC that LinuxCNC has.

If you are familiar with PLC programming then CL might be your preferred solution.

Unfortunately I can't get you links at the moment as the host appears to be down.

skunkworks wrote:

I wrote a comp for our HMC - 4 bit binary 16 speed gear box. (it was my first comp so it is pretty scary )

Aye, no offence, like, but that's pretty messy code.

I will try to knock-up a generic version this evening.