thc − Torch Height Control
Torch Height Control Mesa THC > Encoder > LinuxCNC THC component
The Mesa THC sends a frequency based on the voltage detected to the encoder. The velocity from the encoder is converted to volts with the velocity scale parameter inside the THC component.
The THCAD card sends a frequency at 0 volts so the scale offset parameter is used to zero the calculated voltage.
Component Functions If enabled and torch is on and X + Y velocity is within tolerance of set speed allow the THC to offset the Z axis as needed to maintain voltage.
If enabled and torch is off and the Z axis is moving up remove any correction at a rate not to exceed the rate of movement of the Z axis.
If enabled and torch is off and there is no correction pass the Z position and feed back untouched.
If not enabled pass the Z position and feed back untouched.
Plasma Torch Arc Voltage Signal => 6 x 487k 1% resistors => THC Arc Voltage In
THC Frequency Signal => Encoder #0, pin A (Input)
Plasma Torch Arc OK Signal => input pin
output pin => Plasma Torch Start Arc Contacts
encoder.nn.velocity => thc.encoder-vel (tip voltage)
motion.spindle-on => output pin (start the arc)
thc.arc-ok <= motion.digital-in-00 <= input pin (arc ok signal)
thc.requested-vel <= motion.requested-vel
thc.current-vel <= motion.current-vel
(requires a floating-point thread)
float in Connect to hm2_5i20.0.encoder.00.velocity
float in Connect to motion.current-vel
float in Connect to motion.requested-vel
float in Tip Volts current_vel >= min_velocity requested
float in Velocity Tolerance (Corner Lock)
bit in Connect to motion.spindle-on
bit in Arc OK from Plasma Torch
bit in Enable the THC, if not enabled Z position is passed through
float in Z Motor Position Command in from axis.n.motor-pos-cmd
float out Z Motor Position Command Out
float out Z Position Feedback to Axis
float out The Calculated Volts
bit out When the THC thinks we are at requested speed
float out The Current Offset
float rw The scale to convert the Velocity signal to Volts
float rw The offset of the velocity input at 0 volts
float rw The deviation percent from planned velocity
float rw The deviation of Tip Voltage before correction takes place
float rw The amount of change in user units per period to move Z to correct
GPLv2 or greater