LinuxCNC machine setup selection

BobCAD-CAM is able to manage multiple machine setups in the same project. This is a very useful feature when the workpiece should be cut in several phases with a different fixture for each of them. Below an example with 3 machine setups.

BobCAD V26 - [Multi Setups]_2015-02-09_22-20-50

The generated G-Code file contains all operations in the same file, except if you enable manually only one fixture. So, saving one different G-Code file for each machine setup is possible, but quite painful and risky.

To solve this issue, I have designed a custom BobCAD-CAM postprocessor and a dedicated LinuxCNC/Gmoccapy panel to select from one single G-Code file the operations to be executed for a given machine setup. Also, the Gremlin preview is automatically updated according to the selected machine setup. Here is a video showing how it works:

In the BobCAD-CAM generated G-Code file, the section associated to each machine setup is surrounded by if / elseif / endif statements for dynamic selection.

...
(Machine Setup - 1  Facing)
(FACING)
O100 if  [ #<_selected_setup> EQ 1 ]
T1 M6
G53 G0 Z#<_ini [ AXIS_2 ] SAFE_POSITION>
S15915
M3
G0 X60.150 Y-22.600
M7 (MIST COOLANT)
G0
(Machine Setup - 2  Pocket)
(POCKET)
M5
T2 M6
S3559
M3
M7 (MIST COOLANT)
G0
G0 X5.969 Y.000
G0 Z35.480
...
(NEXT MACHINE SETUP - Machine Setup - 2)
O100 elseif  [ #<_selected_setup> EQ 2 ]
T1 M6
G53 G0 Z#<_ini [ AXIS_2 ] SAFE_POSITION>
....
(NEXT MACHINE SETUP - Machine Setup - 3)
O100 elseif  [ #<_selected_setup> EQ 3 ]
....
G0 Z25.480
G0 Z55.800
O100 endif
M5
M30

The #<_selected_setup> is a custom named parameter linked to a Gmoccapy panel where the setup number can be selected from 1 to 6.

For those who are not using Gmoccapy or LinuxCNC, another option is to get the chosen machine setup by reading an analog input with a M66 statement.

I have spent some hours to configure properly my BobCAD-CAM postprocessor for good result. One tricky aspect is the tools management: if the tool does not change from one machine setup to the next one, the original postprocessor does not include any further tool change statements in the G-Code file. This is not compatible with my O100 if/elseif/endif hack because, the tool change sequence would be issued only for first machine setup. So, I have added a systematic tool change in the following section of the posprocessor:

16. Machine Setup Change
	" "
	"(NEXT MACHINE SETUP - ",setup_name,")"
	" "
	n,"O100 elseif ","[","# EQ ", program_block_5, "]"
	n,t,"M6"
	n,"G53 G0 Z#<_ini","[","AXIS_2","]","SAFE_POSITION>"
	n,s
	n,spindle_on
	n,rapid_move,force_x,xr,force_y,yr,rotary_xyr_angle
	n,program_block_1
	"G0"
	output_rotary_angle

I am not yet fully happy with this solution because I have some unnecessary tool change requests in some situations. But, at least it works, in any case!

I have now to test this modification on the real machine … Stay tuned!

JOG-WHILE-PAUSED

A very useful new feature added to my LInuxCNC config: JOG-WHILE-PAUSED based on M60 remap and Gmoccapy modifications.

I have designed a sharedvar class to exchange data between Gmoccapy and the Python code called by REMAP.
The native pause buttons is fully handled.
Everything looks like a standard M0 behavior, except you have access to all functions as for manual mode during pause.
There is an automatic machine state save/restore included in my modified M60.

http://blog.f1oat.org/linuxcnc/

Installing the Webcam on the CNC-6040

The webcam is mounted along the Z axis. It moves on X and Y, but not Z.
My first idea was to install the webcam on the spindle mount so that it can be moved down to a short distance from the workpiece (too have a large image). However, as the spindle motor height can be adjusted in the mount, it was difficult to find a safe and suitable position for the webcam. So, I went back to the Z axis solution.

20130831_171726

Next step is the vertical alignment of the webcam with Z axis. I used piece of paper (with some writings) attached to a arm  mounted in the spindle. Thanks to this configuration, I can move the target up and down. Then  I tuned adjustments screws of the webcam so that the crosshair center remain on the same point of the target for any Z position. When this is achieved, the webcam axis is perfectly vertical.

20130831_181339

Here, the target at bottom position as seen by the webcam

20130831_181503

And the same target at top position. No noticeable drift => the alignment is ok.

20130831_181507

Next step is the measurement of the offset between the webcam crosshair and the spindle.
I have used a small V-Cutter tool to make a very small hole in a AU4G workpiece. The X/Y position is recorded. The hole as been filled with black color thanks to a soft pencil.

20130831_192751

Then I have moved the X/Y axis to get this hole at the center of the crosshair. The delta with the recorded position is the offset to be configured in LinuxCNC.

20130831_192659

The optical resolution of the webcam at this distance is about 0.1mm per point. I have tried few pointings and achieved an accuracy better than 0.05mm. Surprisingly, that is better than pixel resolution. I think that is possible because we can see when the hole stands between 2 pixels.

A Webcam mounting bracket for machine optical precision pointing

The original idea comes from this post by “catlord”

For my project, I wanted a solution for fine alignment of the webcam axis to the Z axis so that pointing is accurate at any distance. I got inspired by the mounting used for telescope secondary mirror, as shown is this video

For accuracy and stability concern, my design is based on a ball joint. The fine adjustment is done with 3 screws.

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