Machinekit Documentation

HAL Component — THC


thc — Torch Height Control




loadrt thc


Torch Height Control Mesa THC > encoder > Machinekit 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 ⇐ ⇐ input pin (arc ok signal)

HAL Motion Connections thc.requested-vel ⇐ motion.requested-vel

thc.current-vel ⇐ motion.current-vel


thc.N (requires a floating-point thread)


encoder-vel float in - Connect to hm2_5i20.0.encoder.00.velocity

current-vel float in - Connect to motion.current-vel

requested-vel float in - Connect to motion.requested-vel

volts-requested float in - Tip Volts current_vel >= min_velocity requested

vel-tol float in - Velocity Tolerance (Corner Lock)

torch-on bit in - Connect to motion.spindle-on

arc-ok bit in - Arc OK from Plasma Torch

enable bit in - Enable the THC, if not enabled Z position is passed through

z-pos-in float in - Z Motor Position Command in from axis.n.motor-pos-cmd

z-pos-out float out - Z Motor Position Command Out

z-fb-out float out - Z Position Feedback to Axis

volts float out - The Calculated Volts

vel-status bit out - When the THC thinks we are at requested speed

offset-value float out - The Current Offset


vel-scale float rw - The scale to convert the Velocity signal to Volts

scale-offset float rw - The offset of the velocity input at 0 volts

velocity-tol float rw - The deviation percent from planned velocity

voltage-tol float rw - The deviation of Tip Voltage before correction takes place

correction-vel float rw - The amount of change in user units per period to move Z to correct


John Thornton


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