Measurement Only Axes

Hi All,

I am trying to add a measurement only axis to my press brake. The machine is hydraulic (a Promecam) and the bottom bed moves up when the pedal is pushed. I have put a linear scale on the bottom bed so I can measure how much it travels up. I want to measure how far it travels exactly, so I can relate this to the bent angle of the metal.

Anyway, I have added a W axis to the INI and introduced a new joint (joint 1) for it. I can see this in the Axis GUI and it all works nicely, when the encoder moves, the W axis value updates. But when I type "g92 w0" to set a zero point, it doesn't set it to zero. I think this is because the dummy joint I have added for it isn't getting its command position updated. Please see config snippet below:

HAL file excerpt
#
# Setup bed axis (W)
# (this is a DRO only, and just measures the bending depth we actually reach)

# position and velocity feedback
net w-pos-fb <= hm2_7c81.0.encoder.01.position
net w-pos-fb => joint.1.motor-pos-fb

# linear axis encoder, w axis
setp hm2_7c81.0.encoder.01.scale  -200        # this many pulses per mm
setp hm2_7c81.0.encoder.01.filter 0           # no filtering
setp hm2_7c81.0.encoder.01.index-enable true  # encoder has an index

INI file excerpt
#********************
# Axis W - this is the linear scale on the bed
# it needs a dummy joint
#********************
[AXIS_W]
MIN_LIMIT = -200.0
MAX_LIMIT = 200.0
MAX_VELOCITY = 10.0
MAX_ACCELERATION = 50.0
LOCK_VELOCITY = 0.0
LOCK_ACCELERATION = 0.0

[JOINT_1]
TYPE = LINEAR
HOME = 0.0
MAX_VELOCITY = 100.0
MAX_ACCELERATION = 500.0

# axis will appear homed immediately
HOME_SEARCH_VEL = 0.0
HOME_LATCH_VEL  = 0.0
HOME_USE_INDEX  = NO
HOME_SEQUENCE   = 0

FERROR = 99999.0
MIN_FERROR = 99999.0



Any thoughts?

Thanks,
Greg

I think you should use this
linuxcnc.org/docs/html/gui/mdro.html#_ini_file_options

Otherwise LinuxCNC needs to command your motion which you are not doing. 

I'd love to see a config where you simply enter a bend list and it does the maths to determine the commanded position 

Thanks Rod, I wasn't aware of that utility, I shall investigate.

The rest of the machine is under G code control, I use it to set the bending depth and the horizontal and vertical position of the backstops, so I'm not sure a DRO alone will cut the mustard.

Maybe look in to extra joints:

linuxcnc.org/docs/stable/html/man/man9/motion.9.html

You can set the joint to home-in-place in the INI file so LCNC doesn't try to move it.