Velocity output

Krc2 5.6.8.

We are trying to output the real time TCP velocity of CP moves not simply as the path velocity $VEL_ACT, but as a 3D vector velocity. So we want to end up with three real variables say VEL_X, VEL_Y and VEL_Z which would also have sign, which $VEL_ACT does not, as it is the forward path velocity which is always positive. (Unless $VEL_ACT is minus when pressing start minus??)

These VEL_ variables would then be output with three ANOUT instructions. The problem seems to be how to realise the task. Ideally we would need to build a Tech function that could run synchronously in the 12ms interpolation time, but the Function Generator documentation does not give many clues to how this could be accomplished. The other alternative would be to interrogate $POS_ACT cyclically within the SPS and to use the delta of each coordinate to generate the value, but it's doubtful whether such a method would be accurate enough.

Have any of our KUKA Experts got any ideas?

Thanks Panic Mode,

I used your suggestion with minor modifications and it works perfectly. My version looks like this:-

WHILE (NDT_ACTIVE AND NOT(($PRO_STATE1==#P_FREE) OR ($PRO_STATE1==#P_RESET) OR ($PRO_STATE1==#P_END)) AND (VARSTATE ("$POS_ACT")==#INITIALIZED) )
  dT=$TIMER[3] ;SPS cycle time in ms


  IF dT >= 12 then 
    dX = $POS_ACT.X - Old.X ;delta X in mm
    dY = $POS_ACT.Y - Old.Y ;delta Y in mm
    dZ = $POS_ACT.Z - Old.Z ;delta Z in mm


    VelX =  dX/dT ; X velocity in M/s
    VelY =  dY/dT ; Y velocity in M/s
    VelZ =  dZ/dT ; Z velocity in M/s


    Old = $POS_ACT
    $TIMER[3]=0
  Endif
ENDWHILE

It runs in the SPS.SUB in a while loop as long as the flag is active and the programme where the ANOUT instructions are called is in the correct state.

The ANOUT call in the programme looks like this:-

ANOUT ON CHANNEL_3=1.0*VelX
  ANOUT ON CHANNEL_4=1.0*VelY
  ANOUT ON CHANNEL_5=1.0*VelZ

The variables are declared in the $config.dat and are initialised in the programme like this:-

DEF INIT_Vel ( )


  $TIMER_STOP[3]=FALSE
  $TIMER[3]=1
  dT=1
  Old=$POS_ACT
  NDT_ACTIVE=TRUE


END

We are using the analogue outputs via Profibus to drive Beckhoff KL2521 Pulse Train Output Terminals to emulate pulse encoders. Up to 1 M/s on a 500 mm path the accuracy is quite good and better than 0.2mm. Using the while loop in the SPS seems to give a consistent cycle time of 12ms which means we are synchronous with the interpolation cycle.

I understand there is an option with KRC4 to also be able to do this encoder emulation faster but this method on KRC2 with a 12ms IPO seems to be adequate for our purposes.