thc − Torch Height Control
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loadrt thc |
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.
Physical
Connections
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
HAL Plasma
Connections
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)
HAL Motion
Connections
thc.requested-vel <= motion.requested-vel
thc.current-vel <= motion.current-vel
thc (requires a floating-point thread)
thc.encoder-vel float in
Connect to hm2_5i20.0.encoder.00.velocity
thc.current-vel float in
Connect to motion.current-vel
thc.requested-vel float in
Connect to motion.requested-vel
thc.volts-requested float in
Tip Volts current_vel >= min_velocity requested
thc.vel-tol float in
Velocity Tolerance (Corner Lock)
thc.torch-on bit in
Connect to motion.spindle-on
thc.arc-ok bit in
Arc OK from Plasma Torch
thc.enable bit in
Enable the THC, if not enabled Z position is passed through
thc.z-pos-in float in
Z Motor Position Command in from axis.n.motor-pos-cmd
thc.z-pos-out float out
Z Motor Position Command Out
thc.z-fb-out float out
Z Position Feedback to Axis
thc.volts float out
The Calculated Volts
thc.vel-status bit out
When the THC thinks we are at requested speed
thc.offset-value float out
The Current Offset
thc.vel-scale float rw
The scale to convert the Velocity signal to Volts
thc.scale-offset float rw
The offset of the velocity input at 0 volts
thc.velocity-tol float rw
The deviation percent from planned velocity
thc.voltage-tol float rw
The deviation of Tip Voltage before correction takes place
thc.correction-vel float rw
The amount of change in user units per period to move Z to correct
John Thornton
GPLv2 or greater