I'm designing my mill control panel and I think I may have (again!) stepped on a problem.

I have a 3-position switch that controls 2 input lines:

SPINDLE OVERRIDE

FEED OVERRIDE

With the third position being "JOG", but that is considered the default so it doesn't need an explicit control line.

The idea here is that if this switch is in either one of the override positions, the MPG jog handle now controls the respective override functions.

Looking at my lathe control panel code, there is a function to assign a jog handle to an AXIS, but I don't see a way to read the handle as a +/- device I could assign to a variable.

Is there a way to do this?

OK, so research and psudocode:

if (SPINDLE_OVERRIDE_SWITCH == ON) {
     old_axis = mc.mcMpgGetAxis(MPG_INDEX)                                  // Find out what axis the MPG is currently set to and store it   
     mc.mcMpgSetAxis(MPG_INDEX, SOME_UNUSED_AXIS)                 // Set the MPG to an axis we aren't using
     current_override = mcSpindleGetOverride()                                  // Get the current spindle override value
     counts = mc.mcMpgGetInc(MPG_INDEX)                                      // Read how much the handle moved NOT SURE THIS IS RIGHT
     new_override = current_override + (counts * SCALING_FACTOR)  // Compute the delta 
     mc.mcSpindleSetOverride(new_override)                                     // Apply the override to the spindle
     mc.mcMpgSetAxis(MPG_INDEX, old_axis)                                   // Reset the MPG axis
}

I'm not sure how this gets called when the handle moves though. For sure I can call it when the override switch state changes, but how do I call it when the handle moves?

Feed override is similar, using GetFRO / SetFRO.

This isn't quite right.

I can assign the MPG to an unused axis easily enough, then "moving" that axis with the handle results in the machine thinking something moved and updating coordinates on that axis's DRO. If every time I read that axis, I zero it out, whatever the current coordinates are is how far the handle was turned since the last read.

What I don't have is a way to call the script when the handle moves / when that axis moves.

How do I do that?

I could really use some help here....

If you can read the MPG counts through a register you could monitor the register in the PLC script and when it changes if the inputs for spindle override or feed override are on then adjust. Maybe something like this..?

Get register count
if register count does not equal last count then
    if spindle override switch is on
          adjust spindle override
    end
    if feed override switch is on
          adjust feed override
    end
end
last register count = current register count

https://youtu.be/4KEZEf93Qxk

PLC Script

---------------------------------------------------
    --DG 9 April 2022
    -- Enable panel MPG to change override values like a volume control if the selector switch is in the correct position.
    -- This could (should?) be optimized to use less variables to reduce function overhead
    -- but at the moment, it is optimized for readability/comprehension in case Future Me needs
    -- to change it.
    --
    -- NOTE THAT FEED OVERRIDE USES 0-100 CONTROL VALUES AND SPINDLE OVERRIDE USES 0-1
   
            -- handles
            local hAxis_Spindle
            local hAxis_Feed   
            local SelectAxis_Spindle
            local SelectAxis_Feed
            local hEncoderPosition
   
            local MPGHandleRawCount = 0
        local MPGHandleRecenteredCount = 0
            local MPGHandleOverrideDelta = 0
            local OverridePercentChange = 0
            local OverrideValue = 0
   
            -- Grab the switch handles
            hAxis_Spindle, rc = mc.mcSignalGetHandle(inst, mc.ISIG_INPUT2)   
            SelectAxis_Spindle, rc = mc.mcSignalGetState(hAxis_Spindle)
       
            hAxis_Feed, rc = mc.mcSignalGetHandle(inst, mc.ISIG_INPUT3)
            SelectAxis_Feed, rc = mc.mcSignalGetState(hAxis_Feed)
   
            if ((SelectAxis_Feed == 1) or (SelectAxis_Spindle == 1)) then
   
                 -- Grab the current MPG value   
                 hEncoderPosition, rc = mc.mcRegGetHandle(inst,"ESS/Encoders/Encoder_0")
                 MPGHandleRawCount, rc = mc.mcRegGetValue(hEncoderPosition)
   
                 -- Adjust for the zero point (global variable) we set when the HANDLE_MODE switch was activated
                 -- Set by PanelHandleModeChange() in the screen load script
    MPGHandleRecenteredCount = MPGHandleRawCount - GlobalMPGHandleOverrideCurrentOffset
   
                 -- Compute the delta from the global variable where we keep the last known value, and store the current raw count there
                 MPGHandleOverrideDelta = MPGHandleRecenteredCount - GlobalMPGHandleOverrideCurrentValue
                 GlobalMPGHandleOverrideCurrentValue = MPGHandleRecenteredCount     
   
                 -- Convert counts to a percentage change
                 OverridePercentChange = MPGHandleOverrideDelta / GlobalPanelMPGOverrideStepsPerPercent     
   
                 if (SelectAxis_Feed == 1) then
   
                      OverrideValue, rc = mc.mcCntlGetFRO(inst)  -- Get the current FRO
      mc.mcCntlSetLastError(inst, string.format("Current Feed Rate Override: %.4f | Percent Change: %.4f", OverrideValue, OverridePercentChange)) 
                      OverrideValue = OverrideValue + OverridePercentChange
   
                      -- Check if we are out of bounds
                      if (OverrideValue > GlobalPanelFeedrateOverrideMaxPercent) then
                           OverrideValue = GlobalPanelFeedrateOverrideMaxPercent
                           -- We don't want to have to "unwind" the MPG if we keep trying to increase the override value past the left edge
                           -- So change the "zero point" by however far we moved past the left edge
                           GlobalMPGHandleOverrideCurrentOffset = GlobalMPGHandleOverrideCurrentOffset + MPGHandleOverrideDelta
                      elseif (OverrideValue < GlobalPanelFeedrateOverrideMinPercent) then
                           OverrideValue = GlobalPanelFeedrateOverrideMinPercent
                           -- We don't want to have to "unwind" the MPG if we keep trying to increase the override value past the right edge
                           -- So change the "zero point" by however far we moved past the right edge
                           GlobalMPGHandleOverrideCurrentOffset = GlobalMPGHandleOverrideCurrentOffset + MPGHandleOverrideDelta
                      end
      -- mc.mcCntlSetLastError(inst, string.format("Feed Rate Override: %.4f | Zero Point: %.4f", OverrideValue, GlobalMPGHandleOverrideCurrentOffset))
                      rc = mc.mcCntlSetFRO(inst, OverrideValue)
   
                   elseif (SelectAxis_Spindle == 1) then
   
                      OverrideValue, rc = mc.mcSpindleGetOverride(inst) -- Looks like they harmonized the API
      -- We have to convert the percent change for spindle from a 0-100 value to a 0 to 1 value BECAUSE OF COURSE WE *********ING DO
      -- CAN'T USE THE SAME MECHANISM AS THE FEED API THAT WOULD MAKE TOO MUCH SENSE
      OverridePercentChange = OverridePercentChange / 100
      mc.mcCntlSetLastError(inst, string.format("Current Spindle Speed Override: %.4f | Percent Change: %.4f", OverrideValue, OverridePercentChange))
                      OverrideValue = OverrideValue + OverridePercentChange
   
                      -- Check if we are out of bounds
                      if (OverrideValue > GlobalPanelSpindleOverrideMaxPercent) then
                           OverrideValue = GlobalPanelSpindleOverrideMaxPercent
                           -- We don't want to have to "unwind" the MPG if we keep trying to increase the override value past the left edge
                           -- So change the "zero point" by however far we moved past the left edge
                           GlobalMPGHandleOverrideCurrentOffset = GlobalMPGHandleOverrideCurrentOffset + MPGHandleOverrideDelta
                      elseif (OverrideValue < GlobalPanelSpindleOverrideMinPercent) then
                           OverrideValue = GlobalPanelSpindleOverrideMinPercent
                           -- We don't want to have to "unwind" the MPG if we keep trying to increase the override value past the right edge
                           -- So change the "zero point" by however far we moved past the right edge
                           GlobalMPGHandleOverrideCurrentOffset = GlobalMPGHandleOverrideCurrentOffset + MPGHandleOverrideDelta
                      end
                      rc = mc.mcSpindleSetOverride(inst, OverrideValue)
   
                  else
                      -- Should never get here!
                      mc.mcCntlSetLastError(inst, "Mach lost its mind in PLC_PanelHandleOverride - ABORTING") 
                     eStop()
      end
             else
                  -- This is a NO-OP
             end

Screen Load Script

----------------------------------
-- Global Variables to support using panel MPG as
-- a volume knob to adjust overrides

GlobalMPGHandleOverrideCurrentOffset = 0
GlobalMPGHandleOverrideDeltaOffset = 0
GlobalMPGHandleOverrideCurrentValue = 0
GlobalPanelSpindleOverrideMaxPercent = 2.0
GlobalPanelSpindleOverrideMinPercent = 0.5
GlobalPanelFeedrateOverrideMaxPercent = 150
GlobalPanelFeedrateOverrideMinPercent = 50
GlobalPanelMPGOverrideStepsPerPercent = 20

---------------------------------------------------------------
-- The Panel's Override switch changed.
---------------------------------------------------------------
function PanelHandleModeChange()

-- handles
    local hAxis_Spindle
    local hAxis_Feed
   
    local SelectAxis_Spindle
    local SelectAxis_Feed

-- Jog Active Light handle
local hOverrideLight
hOverrideLight, rc = mc.mcSignalGetHandle(inst, mc.OSIG_OUTPUT3) -- Override Light Signal 3

local AxisState
    AxisState, rc = mc.mcMpgGetAxis(inst, MachMpgNumberForPanel)

hAxis_Spindle, rc = mc.mcSignalGetHandle(inst, mc.ISIG_INPUT2)   
        SelectAxis_Spindle, rc = mc.mcSignalGetState(hAxis_Spindle)
   
        hAxis_Feed, rc = mc.mcSignalGetHandle(inst, mc.ISIG_INPUT3)
        SelectAxis_Feed, rc = mc.mcSignalGetState(hAxis_Feed)

-- If both Spindle Override and Axis Ovveride are set, that's a wiring fault
if ((SelectAxis_Spindle == 1) and (SelectAxis_Feed == 1)) then
mc.mcCntlSetLastError(inst, "Spindle and Feed Overrides active simultaniously! WIRING FAULT")
eStop()

-- If both are off, we are back to jog mode.
-- Turn off the override active light,
-- unmap the axis, and re-scan the jog enable/speed switch
elseif ((SelectAxis_Spindle == 0) and (SelectAxis_Feed == 0)) then
mc.mcSignalSetState(hOverrideLight, 0)        -- Turn Override light off
mc.mcMpgSetAxis(inst, MachMpgNumberForPanel, UnmapMPG )    -- Unmap the MPG, so it won't control any axes
mc.mcCntlSetLastError(inst, "Override switch to JOG MODE")  -- Show a message in the Screen Set
PanelSpeedChange() -- Scan jog controls and set state

elseif (SelectAxis_Spindle == 1) then
mc.mcSignalSetState(hOverrideLight, 1)        -- Turn Override light on
mc.mcCntlSetLastError(inst, "Override switch to SPINDLE OVERRIDE")  -- Show a message in the Screen Set
mc.mcMpgSetAxis(inst, MachMpgNumberForPanel, UnmapMPG )    -- Unmap the MPG, so it won't control any axes
-- Grab the current MPG counter and save it in the global variable
-- where the PLC script can see it
hEncoderPosition, rc = mc.mcRegGetHandle(inst,"ESS/Encoders/Encoder_0")
GlobalMPGHandleOverrideCurrentOffset, rc = mc.mcRegGetValue(hEncoderPosition)
GlobalMPGHandleOverrideCurrentValue = 0 -- Reset last known value counter

elseif (SelectAxis_Feed == 1) then
mc.mcSignalSetState(hOverrideLight, 1)        -- Turn Override light on
mc.mcCntlSetLastError(inst, "Override switch to FEED OVERRIDE")  -- Show a message in the Screen Set
mc.mcMpgSetAxis(inst, MachMpgNumberForPanel, UnmapMPG )    -- Unmap the MPG, so it won't control any axes
-- Grab the current MPG counter and save it in the global variable
-- where the PLC script can see it
hEncoderPosition, rc = mc.mcRegGetHandle(inst,"ESS/Encoders/Encoder_0")
GlobalMPGHandleOverrideCurrentOffset, rc = mc.mcRegGetValue(hEncoderPosition)
GlobalMPGHandleOverrideCurrentValue = 0 -- Reset last known value counter

end

end