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.TH THC "9" "2024-03-13" "LinuxCNC Documentation" "HAL Component"
.SH NAME

thc \- Torch Height Control
.SH SYNOPSIS
.HP
.B loadrt thc
.SH DESCRIPTION


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
.br
Plasma Torch Arc Voltage Signal => 6 x 487k 1% resistors => THC Arc Voltage In
.br
THC Frequency Signal => Encoder #0, pin A (Input)
.br
Plasma Torch Arc OK Signal => input pin
.br
output pin => Plasma Torch Start Arc Contacts

HAL Plasma Connections
.br
encoder.nn.velocity => thc.encoder-vel (tip voltage)
.br
spindle.0.on => output pin (start the arc)
.br
thc.arc-ok <= motion.digital-in-00 <= input pin (arc ok signal)

HAL Motion Connections
.br
thc.requested-vel <= motion.requested-vel
.br
thc.current-vel <= motion.current-vel


.SH FUNCTIONS
.TP
\fBthc\fR (requires a floating-point thread)

.SH PINS
.TP
.B thc.encoder-vel\fR float in \fR
Connect to hm2_5i20.0.encoder.00.velocity
.TP
.B thc.current-vel\fR float in \fR
Connect to motion.current-vel
.TP
.B thc.requested-vel\fR float in \fR
Connect to motion.requested-vel
.TP
.B thc.volts-requested\fR float in \fR
Tip Volts current_vel >= min_velocity requested
.TP
.B thc.vel-tol\fR float in \fR
Velocity Tolerance (Corner Lock)
.TP
.B thc.torch-on\fR bit in \fR
Connect to spindle.N.on
.TP
.B thc.arc-ok\fR bit in \fR
Arc OK from Plasma Torch
.TP
.B thc.enable\fR bit in \fR
Enable the THC, if not enabled Z position is passed through
.TP
.B thc.z-pos-in\fR float in \fR
Z Motor Position Command in from axis.n.motor-pos-cmd
.TP
.B thc.z-pos-out\fR float out \fR
Z Motor Position Command Out
.TP
.B thc.z-fb-out\fR float out \fR
Z Position Feedback to Axis
.TP
.B thc.volts\fR float out \fR
The Calculated Volts
.TP
.B thc.vel-status\fR bit out \fR
When the THC thinks we are at requested speed
.TP
.B thc.offset-value\fR float out \fR
The Current Offset
.SH PARAMETERS
.TP
.B thc.vel-scale\fR float rw \fR
The scale to convert the Velocity signal to Volts
.TP
.B thc.scale-offset\fR float rw \fR
The offset of the velocity input at 0 volts
.TP
.B thc.velocity-tol\fR float rw \fR
The deviation percent from planned velocity
.TP
.B thc.voltage-tol\fR float rw \fR
The deviation of Tip Voltage before correction takes place
.TP
.B thc.correction-vel\fR float rw \fR
The amount of change in user units per period to move Z to correct
.SH AUTHOR

John Thornton
.SH LICENSE

GPLv2 or greater