THC for MACH2 update
Posted by
caudlet
on 2003-03-31 11:11:41 UTC
For those of you not yet on the Master5 list:
As of release 16, Art has activated the THC positioning code using
logic inputs to three pins. I have been working on a simple circuit
to detect torch height using the gap voltage and to provide the
correct logic to MACH2. As of last night (Sunday) my newer circuit
is functioning on the testbench. It provides for UP and DOWN logic
outputs via optoisolators, either polarity of torch head voltage, and
logic to turn off the logic outputs when the arc voltage drops to 10%
of the setpoint (adjustable from 68 to 210VDC) and when it exceeds
the upper range. These are safety things to keep the torch
adjustments within a safe range. In addition you can define the
maximum range of excersion in Art's software and the speed at which
it occurs.
As soon as we have the basic circuit and logic tied together, Art has
committed to implementing a method to use a Z reference to do
a "sense" of the material surface prior to each cut. I wish I could
take credit, but one of our other members (Monty) suggest a simple
but elegant method to do the initial head positioning prior to each
cut. Here's how it works: You mount your torch head on a spring
loaded floating head (sub-plate) that will deflect upward if the tip
of the torch contacts the work surface. A sensor is mounted to
detect the upward movement and that will be used to be a home
reference and limit. The floating head does two things. It protects
the torch head from destruction from a possible machine or human
mistake (in code or otherwise) and it allows us to zero the torch tip
and reset the Z axis so we can do precise heights above the work for
piercing and start of cut. The sequence would proceed as follows:
1. The Z is at safe height and XY position is established for a
pierce/cut
2. The head is moved downward to a reference height and the Z axis is
rezeroed at the work surface.
3. The head is retracted to a defined distance above the work and the
Torch is ignited.
4. In the absence of a "arc ready" signal from the Plasma cutter
(not all units have that feature) a timer provides a pause for the
arc to penetrate and stabilize.
5. The THC logic inputs are enabled via another M command (they are
inactive without the torch on as well) and the program is released to
start its cut using the THC positioning.
6. In the circumstance where the Torch voltage is out of spec (Too
high or too low), like would occur if the arc was lost or the torch
runs off the material, the THC external circuit ceases to send logic
signals to MACH2 until proper voltages are again observed. While
this does not deal with stopping XY movement on the loss of arc and
starting a refire sequence it will prevent the head from trying to
lower itself into the work when the arc is lost of the head runs
across a void or off the work.
7. At the end of the cut the sequence is reversed and it all starts
over.
Thats's the plan at this time. We will add more features as the need
becomes evident. It's going to take some practical experience to see
if my detection voltages are correct. It never ceases to amaze me at
the speed that Art can implement the features and changes. He
promised the THC functions "within a week" and delivered them in less
than 24 hours after that promise...wow!
The schematic for the THC will be posted in the next 24hrs in the
files section of Master5 group.
As of release 16, Art has activated the THC positioning code using
logic inputs to three pins. I have been working on a simple circuit
to detect torch height using the gap voltage and to provide the
correct logic to MACH2. As of last night (Sunday) my newer circuit
is functioning on the testbench. It provides for UP and DOWN logic
outputs via optoisolators, either polarity of torch head voltage, and
logic to turn off the logic outputs when the arc voltage drops to 10%
of the setpoint (adjustable from 68 to 210VDC) and when it exceeds
the upper range. These are safety things to keep the torch
adjustments within a safe range. In addition you can define the
maximum range of excersion in Art's software and the speed at which
it occurs.
As soon as we have the basic circuit and logic tied together, Art has
committed to implementing a method to use a Z reference to do
a "sense" of the material surface prior to each cut. I wish I could
take credit, but one of our other members (Monty) suggest a simple
but elegant method to do the initial head positioning prior to each
cut. Here's how it works: You mount your torch head on a spring
loaded floating head (sub-plate) that will deflect upward if the tip
of the torch contacts the work surface. A sensor is mounted to
detect the upward movement and that will be used to be a home
reference and limit. The floating head does two things. It protects
the torch head from destruction from a possible machine or human
mistake (in code or otherwise) and it allows us to zero the torch tip
and reset the Z axis so we can do precise heights above the work for
piercing and start of cut. The sequence would proceed as follows:
1. The Z is at safe height and XY position is established for a
pierce/cut
2. The head is moved downward to a reference height and the Z axis is
rezeroed at the work surface.
3. The head is retracted to a defined distance above the work and the
Torch is ignited.
4. In the absence of a "arc ready" signal from the Plasma cutter
(not all units have that feature) a timer provides a pause for the
arc to penetrate and stabilize.
5. The THC logic inputs are enabled via another M command (they are
inactive without the torch on as well) and the program is released to
start its cut using the THC positioning.
6. In the circumstance where the Torch voltage is out of spec (Too
high or too low), like would occur if the arc was lost or the torch
runs off the material, the THC external circuit ceases to send logic
signals to MACH2 until proper voltages are again observed. While
this does not deal with stopping XY movement on the loss of arc and
starting a refire sequence it will prevent the head from trying to
lower itself into the work when the arc is lost of the head runs
across a void or off the work.
7. At the end of the cut the sequence is reversed and it all starts
over.
Thats's the plan at this time. We will add more features as the need
becomes evident. It's going to take some practical experience to see
if my detection voltages are correct. It never ceases to amaze me at
the speed that Art can implement the features and changes. He
promised the THC functions "within a week" and delivered them in less
than 24 hours after that promise...wow!
The schematic for the THC will be posted in the next 24hrs in the
files section of Master5 group.